diff --git a/.changeset/host-duration-editor.md b/.changeset/host-duration-editor.md
new file mode 100644
index 00000000..32b0a337
--- /dev/null
+++ b/.changeset/host-duration-editor.md
@@ -0,0 +1,7 @@
+---
+'@when/web': patch
+'@when/worker': patch
+'@when/cli': patch
+---
+
+Let hosts change an existing appointment's duration without moving its start time or replacing the booking. Check actual busy-time conflicts while ignoring buffers, daily caps and working hours. Keep calendar/invite updates, duration history and existing edit notifications consistent, and distinguish saved changes from unconfirmed background-update submission.
diff --git a/apps/web/e2e/duration-editor.e2e.ts b/apps/web/e2e/duration-editor.e2e.ts
new file mode 100644
index 00000000..6d0928f9
--- /dev/null
+++ b/apps/web/e2e/duration-editor.e2e.ts
@@ -0,0 +1,473 @@
+import { expect, test, type Page } from '@playwright/test';
+import { parseActionLog } from '@when/db';
+import { signInAsAdmin } from './support/auth.ts';
+import { readAppointment, readQueuedWorkflows } from './support/database.ts';
+import { seedAppointment } from './support/seed.ts';
+
+const postOptions = {
+	headers: { origin: 'http://localhost:4183', accept: 'application/json' },
+	maxRedirects: 0
+};
+const savedWarning =
+	'The duration was saved, but calendar and email update submission could not be confirmed.';
+
+function futureWeekday(offset: number, retry: number): string {
+	const date = new Date();
+	date.setUTCDate(date.getUTCDate() + offset);
+	for (let attempt = 0; attempt <= retry; attempt++) {
+		if (attempt > 0) date.setUTCDate(date.getUTCDate() + 1);
+		while (date.getUTCDay() === 0 || date.getUTCDay() === 6) {
+			date.setUTCDate(date.getUTCDate() + 1);
+		}
+	}
+	return date.toISOString().slice(0, 10);
+}
+
+function durationAction(id: string): string {
+	return `/admin/appointment/${id}?/changeDuration`;
+}
+
+async function openDurationEditor(page: Page) {
+	await page.getByRole('button', { name: 'Appointment actions', exact: true }).click();
+	await page.getByRole('menuitem', { name: 'Change duration', exact: true }).click();
+	const dialog = page.getByRole('dialog', { name: 'Change duration', exact: true });
+	await expect(dialog).toBeVisible();
+	return dialog;
+}
+
+// Evening intervals keep these edits disjoint from the older daytime scheduling cases.
+test('host extends in place outside working hours, touching a neighbor despite buffers and cap', async ({
+	page,
+	request
+}, testInfo) => {
+	const day = futureWeekday(17, testInfo.retry);
+	const original = await seedAppointment({
+		eventTypeId: 'host-rules',
+		status: 'confirmed',
+		start: new Date(`${day}T18:00:00Z`)
+	});
+	const neighbor = await seedAppointment({
+		eventTypeId: 'host-rules',
+		status: 'confirmed',
+		start: new Date(`${day}T19:30:00Z`)
+	});
+	const actionPath = durationAction(original.id);
+	await page.goto(`/appointment/${original.id}?token=${original.cancel_token}`);
+	await page.getByRole('button', { name: 'Appointment actions', exact: true }).click();
+	await expect(page.getByRole('menuitem', { name: 'Change duration', exact: true })).toHaveCount(0);
+	await expect(page.getByRole('dialog', { name: 'Change duration', exact: true })).toHaveCount(0);
+	await page.keyboard.press('Escape');
+	const forbidden = await request.post(actionPath, {
+		...postOptions,
+		form: { duration: '90', token: original.cancel_token, role: 'host', isAdmin: 'true' }
+	});
+	expect(forbidden.status()).toBe(403);
+	const beforeEdit = await readAppointment(original.id);
+	expect(beforeEdit).toEqual(original);
+
+	await signInAsAdmin(page);
+	await page.goto(`/appointment/${original.id}`);
+	await page.emulateMedia({ colorScheme: 'light' });
+	const dialog = await openDurationEditor(page);
+	await expect(dialog.getByLabel('Duration', { exact: true })).toHaveValue('30');
+	await dialog.getByLabel('Duration', { exact: true }).selectOption('90');
+	const desktopScreenshot = await page.screenshot({
+		path: testInfo.outputPath('duration-editor-desktop-light.png')
+	});
+	await testInfo.attach('duration-editor-desktop-light', {
+		body: desktopScreenshot,
+		contentType: 'image/png'
+	});
+	const responsePromise = page.waitForResponse(
+		(response) => response.request().method() === 'POST' && response.url().endsWith(actionPath)
+	);
+	await dialog.getByRole('button', { name: 'Save', exact: true }).click();
+	const response = await responsePromise;
+	const result = await response.json();
+	expect(result).toMatchObject({ type: 'success', status: 200 });
+	expect(result.data).toContain('duration_changed');
+	await expect(dialog.getByRole('status')).toHaveText('Duration saved.');
+	await expect(dialog.getByRole('button', { name: 'Done', exact: true })).toBeEnabled();
+	await expect(dialog.getByLabel('Duration', { exact: true })).toBeDisabled();
+	await expect(dialog.getByRole('button', { name: 'Save', exact: true })).toHaveCount(0);
+	await expect(dialog.getByRole('button', { name: 'Close', exact: true })).toHaveCount(0);
+
+	const saved = await readAppointment(original.id);
+	expect(saved).toMatchObject({
+		id: original.id,
+		start_time: original.start_time,
+		status: original.status,
+		cancel_token: original.cancel_token,
+		origin_id: original.origin_id,
+		video_chat: original.video_chat,
+		video_chat_request: original.video_chat_request,
+		calendar_revision: original.calendar_revision + 1,
+		ics_sequence: original.ics_sequence + 1
+	});
+	expect(Date.parse(saved.end_time) - Date.parse(saved.start_time)).toBe(90 * 60_000);
+	expect(Date.parse(saved.end_time)).toBe(Date.parse(neighbor.start_time));
+	const log = parseActionLog(saved.action_log);
+	expect(log).toHaveLength(parseActionLog(original.action_log).length + 1);
+	expect(log.at(-1)).toMatchObject({
+		action: 'edit',
+		actor: 'host',
+		payload: {
+			metadata: { changes: ['duration_updated'], previous_duration: 30, duration: 90 }
+		}
+	});
+	expect(readQueuedWorkflows(`${original.id}:edited-by-host:${saved.ics_sequence}`)).toEqual([
+		{ workflow_name: 'reconcile-appointment' }
+	]);
+	const unchangedNeighbor = await readAppointment(neighbor.id);
+	expect(unchangedNeighbor).toEqual(neighbor);
+	await dialog.getByRole('button', { name: 'Done', exact: true }).click();
+	await expect(dialog).not.toBeVisible();
+	await expect(page.locator('.detail-primary').filter({ hasText: /6:00.*7:30/ })).toBeVisible();
+	await page.getByText('Activity log', { exact: true }).click();
+	await expect(
+		page.getByText('Duration changed from 30 to 90 minutes', { exact: true })
+	).toBeVisible();
+});
+
+test('actual overlap stays inline and the same dialog can shorten to configured 25, not invented 75', async ({
+	page
+}, testInfo) => {
+	const day = futureWeekday(28, testInfo.retry);
+	const original = await seedAppointment({
+		eventTypeId: 'host-durations',
+		status: 'confirmed',
+		start: new Date(`${day}T18:00:00Z`),
+		durationMinutes: 60
+	});
+	const neighbor = await seedAppointment({
+		eventTypeId: 'host-durations',
+		status: 'confirmed',
+		start: new Date(`${day}T19:15:00Z`)
+	});
+	const actionPath = durationAction(original.id);
+	await signInAsAdmin(page);
+	const unsupported = await page.request.post(actionPath, {
+		...postOptions,
+		form: {
+			duration: '75',
+			currentDuration: '75',
+			id: neighbor.id,
+			start_time: `${day}T09:00:00Z`
+		}
+	});
+	const unsupportedResult = await unsupported.json();
+	expect(unsupportedResult).toMatchObject({ type: 'failure', status: 400 });
+	expect(unsupportedResult.data).toContain('Please pick a valid meeting length.');
+	await page.goto(`/appointment/${original.id}`);
+	const dialog = await openDurationEditor(page);
+	await expect(dialog.getByRole('option', { name: '25 minutes', exact: true })).toHaveCount(1);
+	await expect(dialog.getByRole('option', { name: '75 minutes', exact: true })).toHaveCount(0);
+	await dialog.getByLabel('Duration', { exact: true }).selectOption('90');
+	const rejectedPromise = page.waitForResponse(
+		(response) => response.request().method() === 'POST' && response.url().endsWith(actionPath)
+	);
+	await dialog.getByRole('button', { name: 'Save', exact: true }).click();
+	const rejected = await rejectedPromise;
+	const rejectedResult = await rejected.json();
+	expect(rejectedResult).toMatchObject({ type: 'failure', status: 409 });
+	await expect(dialog.getByRole('alert')).toHaveText(
+		'That length overlaps another appointment or busy event.'
+	);
+	await expect(dialog.getByLabel('Duration', { exact: true })).toHaveValue('90');
+	await expect(dialog.getByLabel('Duration', { exact: true })).toBeEnabled();
+	await expect(dialog.getByRole('button', { name: 'Save', exact: true })).toBeEnabled();
+	await expect(dialog.getByRole('button', { name: 'Close', exact: true })).toBeEnabled();
+	const unchanged = await readAppointment(original.id);
+	expect(unchanged).toEqual(original);
+
+	await dialog.getByLabel('Duration', { exact: true }).selectOption('25');
+	const savedPromise = page.waitForResponse(
+		(response) => response.request().method() === 'POST' && response.url().endsWith(actionPath)
+	);
+	await dialog.getByRole('button', { name: 'Save', exact: true }).click();
+	const savedResponse = await savedPromise;
+	const savedResult = await savedResponse.json();
+	expect(savedResult).toMatchObject({ type: 'success', status: 200 });
+	expect(savedResult.data).toContain('duration_changed');
+	// The browser sends an absolute duration only; identity/start are read by the server.
+	const submittedBody = savedResponse.request().postData();
+	expect(submittedBody).toContain('name="duration"');
+	expect(submittedBody).not.toMatch(/name="(?:id|start|start_time|slot)"/);
+	await expect(dialog.getByRole('status')).toHaveText('Duration saved.');
+	await expect(dialog.getByRole('alert')).toHaveCount(0);
+	await expect(dialog.getByRole('button', { name: 'Done', exact: true })).toBeEnabled();
+	const saved = await readAppointment(original.id);
+	expect(saved.start_time).toBe(original.start_time);
+	expect(Date.parse(saved.end_time) - Date.parse(original.start_time)).toBe(25 * 60_000);
+	const unchangedNeighbor = await readAppointment(neighbor.id);
+	expect(unchangedNeighbor).toEqual(neighbor);
+
+	const noOp = await page.request.post(actionPath, {
+		...postOptions,
+		form: { duration: '25', id: neighbor.id, start_time: `${day}T09:00:00Z` }
+	});
+	const noOpResult = await noOp.json();
+	expect(noOpResult).toMatchObject({ type: 'success', status: 200 });
+	expect(noOpResult.data).toContain('no_change');
+	const afterNoOp = await readAppointment(original.id);
+	expect(afterNoOp).toEqual(saved);
+	await dialog.getByRole('button', { name: 'Done', exact: true }).click();
+	await expect(dialog).not.toBeVisible();
+	await expect(page.locator('.detail-primary').filter({ hasText: /6:00.*6:25/ })).toBeVisible();
+});
+
+test('in-progress edits require a future end; ended pending appointments have no editor', async ({
+	page
+}) => {
+	// Only this case uses a live interval: 15 ends five minutes ago, 30 ten minutes ahead.
+	const start = new Date(Date.now() - 20 * 60_000);
+	const original = await seedAppointment({
+		eventTypeId: 'host-rules',
+		status: 'confirmed',
+		start,
+		durationMinutes: 60
+	});
+	const actionPath = durationAction(original.id);
+	await signInAsAdmin(page);
+	await page.goto(`/appointment/${original.id}`);
+	await expect(page.getByRole('heading', { name: 'In progress', exact: true })).toBeVisible();
+	const dialog = await openDurationEditor(page);
+	await dialog.getByLabel('Duration', { exact: true }).selectOption('15');
+	const rejectedPromise = page.waitForResponse(
+		(response) => response.request().method() === 'POST' && response.url().endsWith(actionPath)
+	);
+	await dialog.getByRole('button', { name: 'Save', exact: true }).click();
+	const rejected = await rejectedPromise;
+	const rejectedResult = await rejected.json();
+	expect(rejectedResult).toMatchObject({ type: 'failure', status: 400 });
+	await expect(dialog.getByRole('alert')).toHaveText('Choose a length that ends in the future.');
+	const unchanged = await readAppointment(original.id);
+	expect(unchanged).toEqual(original);
+	await dialog.getByLabel('Duration', { exact: true }).selectOption('30');
+	const savedPromise = page.waitForResponse(
+		(response) => response.request().method() === 'POST' && response.url().endsWith(actionPath)
+	);
+	await dialog.getByRole('button', { name: 'Save', exact: true }).click();
+	const savedResponse = await savedPromise;
+	const savedResult = await savedResponse.json();
+	expect(savedResult).toMatchObject({ type: 'success', status: 200 });
+	expect(savedResult.data).toContain('duration_changed');
+	await expect(dialog.getByRole('status')).toHaveText('Duration saved.');
+	await expect(dialog.getByRole('button', { name: 'Done', exact: true })).toBeEnabled();
+	const saved = await readAppointment(original.id);
+	expect(saved.start_time).toBe(original.start_time);
+	expect(Date.parse(saved.end_time) - start.getTime()).toBe(30 * 60_000);
+	expect(saved.status).toBe('confirmed');
+	await dialog.getByRole('button', { name: 'Done', exact: true }).click();
+	await expect(dialog).not.toBeVisible();
+	await expect(page.getByRole('heading', { name: 'In progress', exact: true })).toBeVisible();
+
+	const endedPending = await seedAppointment({
+		eventTypeId: 'host-rules',
+		status: 'pending',
+		start: new Date(start.getTime() - 2 * 60 * 60_000)
+	});
+	await page.goto(`/appointment/${endedPending.id}`);
+	await expect(page.getByRole('heading', { name: 'Pending', exact: true })).toBeVisible();
+	await page.getByRole('button', { name: 'Appointment actions', exact: true }).click();
+	await expect(page.getByRole('menuitem', { name: 'Change duration', exact: true })).toHaveCount(0);
+	await expect(page.getByRole('dialog', { name: 'Change duration', exact: true })).toHaveCount(0);
+	const gated = await page.request.post(durationAction(endedPending.id), {
+		...postOptions,
+		form: { duration: '90' }
+	});
+	const gatedResult = await gated.json();
+	expect(gatedResult).toMatchObject({ type: 'failure', status: 400 });
+	expect(gatedResult.data).toContain('This appointment cannot be edited.');
+	const unchangedPending = await readAppointment(endedPending.id);
+	expect(unchangedPending).toEqual(endedPending);
+});
+
+test('a saved-warning receipt waits for explicit reload and cannot blindly resubmit', async ({
+	page
+}, testInfo) => {
+	const day = futureWeekday(38, testInfo.retry);
+	const original = await seedAppointment({
+		eventTypeId: 'host-rules',
+		status: 'confirmed',
+		start: new Date(`${day}T18:00:00Z`)
+	});
+	const actionPath = durationAction(original.id);
+	await signInAsAdmin(page);
+	await page.setViewportSize({ width: 320, height: 720 });
+	await page.emulateMedia({ colorScheme: 'dark' });
+	await page.goto(`/appointment/${original.id}`);
+	let submissions = 0;
+	const refreshRequests: string[] = [];
+	page.on('request', (request) => {
+		const path = new URL(request.url()).pathname;
+		if (
+			request.method() === 'GET' &&
+			(path === `/appointment/${original.id}` || path === `/appointment/${original.id}/__data.json`)
+		) {
+			refreshRequests.push(request.url());
+		}
+	});
+	await page.route(`**${actionPath}`, async (route) => {
+		submissions++;
+		const realResponse = await route.fetch();
+		const realResult = await realResponse.json();
+		expect(realResult).toMatchObject({ type: 'success', status: 200 });
+		expect(realResult.data).toContain('duration_changed');
+		// Public SvelteKit ActionResult wire format: data is a devalue flat table.
+		// This simulates a saved-warning RECEIPT after a real commit, not a queue failure.
+		await route.fulfill({
+			status: 500,
+			contentType: 'application/json',
+			body: JSON.stringify({
+				type: 'failure',
+				status: 500,
+				data: JSON.stringify([{ error: 1, durationSaved: 2 }, savedWarning, true])
+			})
+		});
+	});
+	const dialog = await openDurationEditor(page);
+	await dialog.getByLabel('Duration', { exact: true }).selectOption('90');
+	await dialog.getByRole('button', { name: 'Save', exact: true }).click();
+	await expect(dialog.getByRole('alert')).toHaveText(savedWarning);
+	await expect(dialog.getByLabel('Duration', { exact: true })).toBeDisabled();
+	await expect(dialog.getByRole('button', { name: 'Save', exact: true })).toHaveCount(0);
+	await expect(dialog.getByRole('button', { name: 'Close', exact: true })).toHaveCount(0);
+	await expect(
+		dialog.getByRole('button', { name: 'Reload appointment', exact: true })
+	).toBeEnabled();
+	const saved = await readAppointment(original.id);
+	expect(Date.parse(saved.end_time) - Date.parse(original.start_time)).toBe(90 * 60_000);
+	expect(saved.ics_sequence).toBe(original.ics_sequence + 1);
+	const mobileScreenshot = await page.screenshot({
+		path: testInfo.outputPath('duration-editor-saved-warning-mobile-320-dark.png')
+	});
+	await testInfo.attach('duration-editor-saved-warning-mobile-320-dark', {
+		body: mobileScreenshot,
+		contentType: 'image/png'
+	});
+	await page.keyboard.press('Escape');
+	await expect(dialog.getByRole('alert')).toHaveText(savedWarning);
+	expect(refreshRequests).toEqual([]);
+	const reload = page.waitForNavigation({ waitUntil: 'load' });
+	await dialog.getByRole('button', { name: 'Reload appointment', exact: true }).click();
+	await reload;
+	await expect(dialog).not.toBeVisible();
+	await expect(page.locator('.detail-primary').filter({ hasText: /6:00.*7:30/ })).toBeVisible();
+	await expect(page.getByRole('alert')).toHaveCount(0);
+	expect(refreshRequests).toHaveLength(1);
+	const reopened = await openDurationEditor(page);
+	await expect(reopened.getByLabel('Duration', { exact: true })).toHaveValue('90');
+	await expect(reopened.getByRole('alert')).toHaveCount(0);
+	expect(submissions).toBe(1);
+});
+
+test('an aborted action reports uncertainty, not rollback, and never automatically repeats', async ({
+	page
+}, testInfo) => {
+	const day = futureWeekday(8, testInfo.retry);
+	const original = await seedAppointment({
+		eventTypeId: 'host-rules',
+		status: 'confirmed',
+		start: new Date(`${day}T18:00:00Z`)
+	});
+	const actionPath = durationAction(original.id);
+	await signInAsAdmin(page);
+	await page.goto(`/appointment/${original.id}`);
+	let submissions = 0;
+	await page.route(`**${actionPath}`, async (route) => {
+		submissions++;
+		// Controlled transport loss before forwarding; a real lost response need not roll back.
+		await route.abort('failed');
+	});
+	const dialog = await openDurationEditor(page);
+	await dialog.getByLabel('Duration', { exact: true }).selectOption('90');
+	await dialog.getByRole('button', { name: 'Save', exact: true }).click();
+	await expect(dialog.getByRole('alert')).toHaveText(
+		'Could not confirm whether the duration was saved. Reload the page to check before making another change.'
+	);
+	await expect(dialog).not.toContainText(/save failed|rolled back|not saved/i);
+	await expect(dialog.getByRole('status')).toHaveCount(0);
+	await expect(dialog.getByLabel('Duration', { exact: true })).toBeDisabled();
+	await expect(dialog.getByRole('button', { name: 'Save', exact: true })).toHaveCount(0);
+	await expect(dialog.getByRole('button', { name: 'Close', exact: true })).toHaveCount(0);
+	await expect(dialog.getByRole('button', { name: 'Reload to check', exact: true })).toBeEnabled();
+	const unchanged = await readAppointment(original.id);
+	expect(unchanged).toEqual(original);
+	await page.keyboard.press('Escape');
+	await expect(dialog.getByRole('alert')).toContainText('Could not confirm whether');
+	await dialog.getByRole('button', { name: 'Reload to check', exact: true }).click();
+	await expect(dialog).not.toBeVisible();
+	await expect(page.locator('.detail-primary').filter({ hasText: /6:00.*6:30/ })).toBeVisible();
+	expect(submissions).toBe(1);
+});
+
+test('known saved survives unavailable refresh until the user explicitly acknowledges it', async ({
+	page
+}, testInfo) => {
+	const day = futureWeekday(55, testInfo.retry);
+	const original = await seedAppointment({
+		eventTypeId: 'host-rules',
+		status: 'confirmed',
+		start: new Date(`${day}T18:00:00Z`)
+	});
+	const actionPath = durationAction(original.id);
+	const detailPath = `/appointment/${original.id}`;
+	await signInAsAdmin(page);
+	await page.goto(detailPath);
+	let submissions = 0;
+	page.on('request', (request) => {
+		if (request.method() === 'POST' && request.url().endsWith(actionPath)) submissions++;
+	});
+	const refreshRequests: string[] = [];
+	// Public HTTP failures only: an automatic data request would abort and could destroy
+	// the receipt. An explicitly acknowledged document reload gets a bounded error page.
+	await page.route(
+		(url) => url.pathname === detailPath || url.pathname === `${detailPath}/__data.json`,
+		async (route) => {
+			const request = route.request();
+			refreshRequests.push(request.url());
+			if (request.isNavigationRequest()) {
+				await route.fulfill({
+					status: 503,
+					contentType: 'text/html',
+					body: '<!doctype html><title>Reload unavailable</title><h1>Appointment reload unavailable</h1>'
+				});
+			} else {
+				await route.abort('failed');
+			}
+		}
+	);
+	const dialog = await openDurationEditor(page);
+	await dialog.getByLabel('Duration', { exact: true }).selectOption('90');
+	const responsePromise = page.waitForResponse(
+		(response) => response.request().method() === 'POST' && response.url().endsWith(actionPath)
+	);
+	await dialog.getByRole('button', { name: 'Save', exact: true }).click();
+	const response = await responsePromise;
+	const result = await response.json();
+	expect(result).toMatchObject({ type: 'success', status: 200 });
+	expect(result.data).toContain('duration_changed');
+	await expect(dialog.getByRole('status')).toHaveText('Duration saved.');
+	const saved = await readAppointment(original.id);
+	expect(Date.parse(saved.end_time) - Date.parse(original.start_time)).toBe(90 * 60_000);
+	expect(saved.calendar_revision).toBe(original.calendar_revision + 1);
+	await expect(dialog.getByRole('alert')).toHaveCount(0);
+	await expect(dialog).not.toContainText(/could not confirm whether|save failed|not saved/i);
+	await expect(dialog.getByRole('button', { name: 'Save', exact: true })).toHaveCount(0);
+	await expect(dialog.getByRole('button', { name: 'Close', exact: true })).toHaveCount(0);
+	await expect(dialog.getByRole('button', { name: 'Done', exact: true })).toBeEnabled();
+	await page.keyboard.press('Escape');
+	await expect(dialog.getByRole('status')).toHaveText('Duration saved.');
+	expect(refreshRequests).toEqual([]);
+	expect(submissions).toBe(1);
+
+	await dialog.getByRole('button', { name: 'Done', exact: true }).click();
+	await expect(page.getByRole('heading', { name: 'Appointment reload unavailable' })).toBeVisible();
+	await expect(dialog).not.toBeVisible();
+	expect(refreshRequests).toHaveLength(1);
+	await expect(page.locator('body')).not.toContainText(/save failed|not saved|rolled back/i);
+	const afterAcknowledgement = await readAppointment(original.id);
+	expect(afterAcknowledgement).toEqual(saved);
+	expect(submissions).toBe(1);
+});
diff --git a/apps/web/src/lib/components/AppointmentActions.svelte b/apps/web/src/lib/components/AppointmentActions.svelte
index 3ad8e76c..7d592644 100644
--- a/apps/web/src/lib/components/AppointmentActions.svelte
+++ b/apps/web/src/lib/components/AppointmentActions.svelte
@@ -24,6 +24,7 @@
 		onGenerateVideoChat?: () => void;
 		onRemoveVideoChat?: () => void;
 		onEditVideoChat?: () => void;
+		onEditDuration?: () => void;
 		isEditable?: boolean;
 	}
 
@@ -43,6 +44,7 @@
 		onGenerateVideoChat,
 		onRemoveVideoChat,
 		onEditVideoChat,
+		onEditDuration,
 		isEditable = false
 	}: Props = $props();
 
@@ -122,6 +124,20 @@
 						<div {...wrapperProps}>
 							<div {...props} class="ba-menu">
 								{#if isHost && isEditable}
+									{#if onEditDuration}
+										<DropdownMenu.Item
+											onSelect={() => {
+												menuOpen = false;
+												onEditDuration();
+											}}
+										>
+											{#snippet child({ props: itemProps })}
+												<button {...itemProps} type="button" class="action-item"
+													>Change duration</button
+												>
+											{/snippet}
+										</DropdownMenu.Item>
+									{/if}
 									{#if onEditNote && !hasNote}
 										<DropdownMenu.Item
 											onSelect={() => {
diff --git a/apps/web/src/lib/components/AppointmentLog.svelte b/apps/web/src/lib/components/AppointmentLog.svelte
index 48c8a7a4..de44a794 100644
--- a/apps/web/src/lib/components/AppointmentLog.svelte
+++ b/apps/web/src/lib/components/AppointmentLog.svelte
@@ -124,6 +124,14 @@
 										Note updated
 									{:else if changes.includes('note_removed')}
 										Note removed
+									{:else if changes.includes('duration_updated')}
+										{@const previousDuration = entry.payload?.metadata?.previous_duration}
+										{@const duration = entry.payload?.metadata?.duration}
+										{#if typeof previousDuration === 'number' && Number.isFinite(previousDuration) && previousDuration > 0 && typeof duration === 'number' && Number.isFinite(duration) && duration > 0}
+											Duration changed from {previousDuration} to {duration} minutes
+										{:else}
+											Duration changed
+										{/if}
 									{:else}
 										Details updated
 									{/if}
diff --git a/apps/web/src/lib/components/DurationEditor.svelte b/apps/web/src/lib/components/DurationEditor.svelte
new file mode 100644
index 00000000..e3714b77
--- /dev/null
+++ b/apps/web/src/lib/components/DurationEditor.svelte
@@ -0,0 +1,280 @@
+<script lang="ts">
+	import { Dialog } from 'bits-ui';
+	import { deserialize } from '$app/forms';
+	import { untrack } from 'svelte';
+
+	interface Props {
+		open?: boolean;
+		appointmentId: string;
+		currentDuration: number;
+		durations: number[];
+	}
+
+	let { open = $bindable(false), appointmentId, currentDuration, durations }: Props = $props();
+	const durationId = $props.id();
+
+	type Outcome = 'editing' | 'duration_changed' | 'no_change' | 'updates_unconfirmed' | 'uncertain';
+
+	let draft = $state(0);
+	let choices = $state<number[]>([]);
+	let saving = $state(false);
+	let error = $state<string | null>(null);
+	let outcome = $state<Outcome>('editing');
+
+	$effect(() => {
+		if (open) {
+			// Read projected choices only on opening, not when props change.
+			untrack(() => {
+				draft = currentDuration;
+				choices = [...durations];
+				error = null;
+				outcome = 'editing';
+			});
+		}
+	});
+
+	async function save(event: SubmitEvent) {
+		event.preventDefault();
+		if (saving || outcome !== 'editing') return;
+
+		saving = true;
+		error = null;
+		const form = new FormData();
+		form.set('duration', String(draft));
+
+		try {
+			let result: ReturnType<typeof deserialize>;
+			try {
+				const response = await fetch(`/admin/appointment/${appointmentId}?/changeDuration`, {
+					method: 'POST',
+					headers: { accept: 'application/json', 'x-sveltekit-action': 'true' },
+					body: form
+				});
+				const body = await response.text();
+				result = deserialize(body);
+			} catch {
+				outcome = 'uncertain';
+				return;
+			}
+
+			if (
+				result?.type === 'success' &&
+				(result.data?.success === 'duration_changed' || result.data?.success === 'no_change')
+			) {
+				outcome = result.data.success;
+			} else if (result?.type === 'failure' && result.data?.durationSaved === true) {
+				outcome = 'updates_unconfirmed';
+			} else if (result?.type === 'failure' && typeof result.data?.error === 'string') {
+				error = result.data.error;
+				return;
+			} else {
+				// Redirects, error envelopes and unrecognized data do not establish whether a write happened.
+				outcome = 'uncertain';
+				return;
+			}
+		} finally {
+			saving = false;
+		}
+	}
+</script>
+
+<Dialog.Root
+	bind:open={
+		() => open,
+		(value) => {
+			if (!saving && outcome === 'editing') open = value;
+		}
+	}
+>
+	<Dialog.Portal>
+		<Dialog.Overlay>
+			{#snippet child({ props })}
+				<div {...props} class="dialog-overlay"></div>
+			{/snippet}
+		</Dialog.Overlay>
+		<Dialog.Content>
+			{#snippet child({ props })}
+				<div {...props} class="duration-editor">
+					<Dialog.Title>
+						{#snippet child({ props: titleProps })}
+							<h2 {...titleProps}>Change duration</h2>
+						{/snippet}
+					</Dialog.Title>
+					<Dialog.Description>
+						{#snippet child({ props: descriptionProps })}
+							<p {...descriptionProps}>
+								The start time stays the same. Calendar and email updates will be requested when the
+								duration changes.
+							</p>
+						{/snippet}
+					</Dialog.Description>
+
+					<form onsubmit={save} aria-busy={saving}>
+						<label for={durationId}>Duration</label>
+						<select
+							id={durationId}
+							name="duration"
+							bind:value={draft}
+							disabled={saving || outcome !== 'editing'}
+						>
+							{#each choices as minutes (minutes)}
+								<option value={minutes}>{minutes} minutes</option>
+							{/each}
+						</select>
+
+						{#if error}
+							<p class="error" role="alert">{error}</p>
+						{/if}
+						{#if outcome === 'duration_changed'}
+							<p role="status">Duration saved.</p>
+						{:else if outcome === 'no_change'}
+							<p role="status">Duration unchanged.</p>
+						{:else if outcome === 'updates_unconfirmed'}
+							<p class="warning" role="alert">
+								The duration was saved, but calendar and email update submission could not be
+								confirmed.
+							</p>
+						{:else if outcome === 'uncertain'}
+							<p class="warning" role="alert">
+								Could not confirm whether the duration was saved. Reload the page to check before
+								making another change.
+							</p>
+						{/if}
+
+						<div class="dialog-actions">
+							{#if outcome === 'editing'}
+								<button type="submit" class="save" disabled={saving}>
+									{#if saving}Saving…{:else}Save{/if}
+								</button>
+								<Dialog.Close>
+									{#snippet child({ props: closeProps })}
+										<button {...closeProps} type="button" disabled={saving}>Close</button>
+									{/snippet}
+								</Dialog.Close>
+							{:else}
+								<button type="button" disabled={saving} onclick={() => window.location.reload()}>
+									{#if outcome === 'uncertain'}Reload to check{:else if outcome === 'updates_unconfirmed'}Reload
+										appointment{:else}Done{/if}
+								</button>
+							{/if}
+						</div>
+					</form>
+				</div>
+			{/snippet}
+		</Dialog.Content>
+	</Dialog.Portal>
+</Dialog.Root>
+
+<style>
+	.dialog-overlay {
+		position: fixed;
+		inset: 0;
+		background: color-mix(in srgb, var(--when-color-text) 40%, transparent);
+		z-index: 200;
+	}
+
+	.duration-editor {
+		position: fixed;
+		top: 50%;
+		left: 50%;
+		transform: translate(-50%, -50%);
+		z-index: 201;
+		box-sizing: border-box;
+		width: min(calc(100vw - var(--space-7) * 2), calc(var(--space-10) * 7));
+		max-height: calc(100dvh - var(--space-7) * 2);
+		overflow-y: auto;
+		display: flex;
+		flex-direction: column;
+		gap: var(--space-5);
+		padding: var(--space-6);
+		border: var(--space-1) solid var(--color-border);
+		border-radius: var(--radius-md);
+		background: var(--color-surface);
+		color: var(--when-color-text);
+		box-shadow: var(--shadow-card);
+	}
+
+	h2 {
+		margin: 0;
+		font-size: var(--font-size-xl);
+	}
+
+	p {
+		margin: 0;
+		color: var(--color-text-secondary);
+		font-size: var(--font-size-md);
+		line-height: 1.5;
+	}
+
+	form,
+	label {
+		display: flex;
+		flex-direction: column;
+		gap: var(--space-4);
+		font-size: var(--font-size-md);
+	}
+
+	select,
+	button {
+		min-height: calc(var(--space-8) + var(--space-4));
+		padding: var(--space-3) var(--space-5);
+		border: var(--space-1) solid var(--color-border-strong);
+		border-radius: var(--radius);
+		background: var(--color-surface);
+		color: var(--when-color-text);
+		font: inherit;
+	}
+
+	button {
+		cursor: pointer;
+		font-weight: 600;
+	}
+
+	button:hover:not(:disabled) {
+		background: var(--color-surface-muted);
+	}
+
+	button.save {
+		background: var(--when-color-primary);
+		border-color: var(--when-color-primary);
+		color: var(--when-color-text-on-primary);
+	}
+
+	button.save:hover:not(:disabled) {
+		background: var(--when-color-primary);
+	}
+
+	button:disabled,
+	select:disabled {
+		cursor: not-allowed;
+		color: var(--color-text-disabled);
+	}
+
+	button:focus-visible,
+	select:focus-visible {
+		outline: var(--space-1) solid var(--when-color-primary);
+		outline-offset: var(--space-1);
+		box-shadow: var(--shadow-focus);
+	}
+
+	.dialog-actions {
+		display: flex;
+		flex-wrap: wrap;
+		gap: var(--space-3);
+	}
+
+	.error,
+	.warning {
+		padding: var(--space-4);
+		border: var(--space-1) solid var(--color-danger-border);
+		border-radius: var(--radius);
+		background: var(--color-danger-bg);
+		color: var(--color-danger-strong);
+	}
+
+	.warning {
+		border-color: var(--color-warning-border);
+		background: var(--color-warning-bg);
+		color: var(--color-warning-strong);
+	}
+</style>
diff --git a/apps/web/src/lib/server/appointment/access.ts b/apps/web/src/lib/server/appointment/access.ts
index 546280d0..962dbc34 100644
--- a/apps/web/src/lib/server/appointment/access.ts
+++ b/apps/web/src/lib/server/appointment/access.ts
@@ -51,6 +51,10 @@ export function isRescheduleAllowed(
 	return now.getTime() + minimumNoticeMinutes * 60 * 1000 <= startMs;
 }
 
+export function isEditAllowed(row: Pick<Appointment, 'end_time' | 'status'>, now: Date): boolean {
+	return ACTIVE_STATUSES.has(row.status) && now.getTime() < Date.parse(row.end_time);
+}
+
 export type ViewableRow = WindowedRow & Pick<Appointment, 'origin_id' | 'cancel_token'>;
 
 export async function isViewAllowed(
diff --git a/apps/web/src/lib/server/appointment/change-duration.test.ts b/apps/web/src/lib/server/appointment/change-duration.test.ts
new file mode 100644
index 00000000..afcdb2f2
--- /dev/null
+++ b/apps/web/src/lib/server/appointment/change-duration.test.ts
@@ -0,0 +1,578 @@
+import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
+import { sql } from 'kysely';
+import {
+	openDb,
+	parseActionLog,
+	replaceCalendarBusy,
+	runMigrations,
+	withWriteTransaction,
+	type Appointment,
+	type NewAppointment
+} from '@when/db';
+import { validConfig } from '$lib/server/__fixtures__/valid-config';
+import { changeAppointmentDuration } from './change-duration';
+import { editAppointment } from './edit';
+import type { AppointmentContext } from './context';
+
+vi.mock('../workflow', () => ({ enqueueAppointmentReconciliation: vi.fn() }));
+import { enqueueAppointmentReconciliation } from '../workflow';
+
+const start = '2099-01-04T15:07:00Z';
+const initialHistory = [{ action: 'create', actor: 'guest', at: '2098-12-01T12:00:00Z' }];
+const baseRow: NewAppointment = {
+	id: 'duration',
+	event_type_id: '30-min-chat',
+	start_time: start,
+	end_time: '2099-01-04T15:37:00Z',
+	status: 'confirmed',
+	cancel_token: 'unchanged-token',
+	origin_id: 'original-appointment',
+	guest_name: 'Guest',
+	guest_email: 'guest@example.com',
+	guest_timezone: 'Pacific/Auckland',
+	guest_answers: JSON.stringify({ goals: 'Keep these answers' }),
+	location: 'Existing location',
+	note: 'Existing note',
+	video_chat: 'https://video.example/keep',
+	video_chat_request: 'generate',
+	external_event_id: 'published-event',
+	external_calendar_id: 'my-google-cal',
+	calendar_revision: 7,
+	calendar_synced_revision: 7,
+	ics_sequence: 4,
+	has_possible_conflict: 1,
+	meeting_snapshot: JSON.stringify(validConfig.meetings['30-min-chat']),
+	action_log: JSON.stringify(initialHistory),
+	created_at: '2098-12-01 12:00:00',
+	updated_at: '2098-12-01 12:00:00'
+};
+
+let db: ReturnType<typeof openDb>;
+let cfg: typeof validConfig;
+let now: string;
+let statements: string[];
+
+function context(): AppointmentContext {
+	return { db, cfg, clock: { now: () => new Date(now), nowMs: () => Date.parse(now) } };
+}
+
+async function seed(changes: Partial<NewAppointment> = {}) {
+	await db
+		.insertInto('appointments')
+		.values({ ...baseRow, ...changes })
+		.execute();
+}
+
+async function row(id = baseRow.id) {
+	const saved = await db
+		.selectFrom('appointments')
+		.selectAll()
+		.where('id', '=', id)
+		.executeTakeFirstOrThrow();
+	return saved;
+}
+
+async function change(durationMinutes: number) {
+	const result = await changeAppointmentDuration(context(), {
+		appointmentId: baseRow.id,
+		durationMinutes
+	});
+	return result;
+}
+
+async function expectUnwritten(before: Appointment) {
+	const saved = await row();
+	expect(saved).toEqual(before);
+	expect(enqueueAppointmentReconciliation).not.toHaveBeenCalled();
+}
+
+beforeEach(async () => {
+	const root = openDb(':memory:');
+	await runMigrations(root);
+	statements = [];
+	db = root.withPlugin({
+		transformQuery({ node, queryId }) {
+			statements.push(root.getExecutor().compileQuery(node, queryId).sql);
+			return node;
+		},
+		async transformResult({ result }) {
+			return result;
+		}
+	});
+	cfg = structuredClone(validConfig);
+	now = '2099-01-04T14:00:00Z';
+	vi.mocked(enqueueAppointmentReconciliation).mockReset();
+	vi.mocked(enqueueAppointmentReconciliation).mockResolvedValue(undefined);
+});
+
+afterEach(async () => {
+	vi.restoreAllMocks();
+	await db.destroy();
+});
+
+describe('changeAppointmentDuration: one in-place host edit', () => {
+	test.each([
+		{ status: 'pending', video_chat_request: null },
+		{ status: 'pending', video_chat_request: 'generate' },
+		{ status: 'pending', video_chat_request: 'suppress' },
+		{ status: 'confirmed', video_chat_request: null },
+		{ status: 'confirmed', video_chat_request: 'generate' },
+		{ status: 'confirmed', video_chat_request: 'suppress' }
+	] as const)(
+		'preserves every non-duration field for $status / $video_chat_request',
+		async (fields) => {
+			await seed(fields);
+			const before = await row();
+			const result = await change(60);
+			const saved = await row();
+
+			expect(result).toEqual({ ok: true, outcome: 'updated', appointment: saved });
+			expect(saved).toEqual({
+				...before,
+				end_time: '2099-01-04T16:07:00Z',
+				calendar_revision: before.calendar_revision + 1,
+				ics_sequence: before.ics_sequence + 1,
+				updated_at: saved.updated_at,
+				action_log: saved.action_log
+			});
+			expect(saved.updated_at).not.toBe(before.updated_at);
+			expect(parseActionLog(saved.action_log)).toEqual([
+				...initialHistory,
+				{
+					action: 'edit',
+					actor: 'host',
+					at: new Date(now).toISOString(),
+					payload: {
+						metadata: { changes: ['duration_updated'], previous_duration: 30, duration: 60 }
+					}
+				}
+			]);
+			const appointments = await db.selectFrom('appointments').selectAll().execute();
+			expect(appointments).toEqual([saved]);
+			expect(enqueueAppointmentReconciliation).toHaveBeenCalledExactlyOnceWith(
+				saved,
+				'edited-by-host'
+			);
+		}
+	);
+
+	test.each([15, 45, 60, 90, 120, 180, 240, 300])(
+		'accepts application host choice %i as total minutes from the original start',
+		async (duration) => {
+			await seed();
+			const result = await change(duration);
+			const saved = await row();
+			expect(result).toEqual({ ok: true, outcome: 'updated', appointment: saved });
+			expect(saved.start_time).toBe(start);
+			expect(saved.end_time).toBe(
+				Temporal.Instant.from(start).add({ minutes: duration }).toString()
+			);
+		}
+	);
+
+	test.each([20, 40, 75, 360])(
+		'accepts configured extra/default %i outside the application choices',
+		async (duration) => {
+			cfg.meetings['30-min-chat'].duration_minutes = 40;
+			cfg.meetings['30-min-chat'].additional_duration_minutes = [20, 75, 360];
+			await seed();
+			const result = await change(duration);
+			expect(result).toMatchObject({ ok: true, outcome: 'updated' });
+			const saved = await row();
+			expect(saved.end_time).toBe(
+				Temporal.Instant.from(start).add({ minutes: duration }).toString()
+			);
+		}
+	);
+
+	test.each([30, 85])(
+		'keeping current %i minutes performs no write, conflict read, history append or enqueue',
+		async (duration) => {
+			await seed({ end_time: Temporal.Instant.from(start).add({ minutes: duration }).toString() });
+			await replaceCalendarBusy(db, 'my-google-cal', [{ start, end: '2099-01-04T20:00:00Z' }]);
+			const before = await row();
+			statements.length = 0;
+			const result = await change(duration);
+
+			expect(result).toEqual({ ok: true, outcome: 'unchanged', appointment: before });
+			expect(statements).toEqual([
+				'BEGIN IMMEDIATE',
+				'select * from "appointments" where "id" = ?',
+				'COMMIT'
+			]);
+			await expectUnwritten(before);
+		}
+	);
+
+	test('rereads the current row instead of overwriting newer omitted fields or using stale duration', async () => {
+		await seed();
+		const page = await row();
+		await db
+			.updateTable('appointments')
+			.set({
+				end_time: '2099-01-04T16:32:00Z',
+				note: 'Newer note',
+				location: 'Newer location',
+				video_chat: 'https://video.example/newer',
+				video_chat_request: 'suppress',
+				guest_answers: '{"new":"answer"}',
+				external_event_id: 'newer-reference',
+				calendar_revision: 9,
+				ics_sequence: 6
+			})
+			.where('id', '=', page.id)
+			.execute();
+		const fresh = await row();
+		const result = await change(60);
+		const saved = await row();
+		expect(result).toEqual({ ok: true, outcome: 'updated', appointment: saved });
+		expect(saved).toEqual({
+			...fresh,
+			end_time: '2099-01-04T16:07:00Z',
+			calendar_revision: 10,
+			ics_sequence: 7,
+			action_log: saved.action_log,
+			updated_at: saved.updated_at
+		});
+		expect(parseActionLog(saved.action_log).at(-1)?.payload?.metadata).toEqual({
+			changes: ['duration_updated'],
+			previous_duration: 85,
+			duration: 60
+		});
+	});
+
+	test('concurrent identical saves serialize to one update and one unchanged result, not two revisions', async () => {
+		await seed();
+		const results = await Promise.all([change(60), change(60)]);
+		expect(results.map((result) => result.ok && result.outcome).sort()).toEqual([
+			'unchanged',
+			'updated'
+		]);
+		const saved = await row();
+		expect(saved).toMatchObject({
+			end_time: '2099-01-04T16:07:00Z',
+			calendar_revision: 8,
+			ics_sequence: 5
+		});
+		expect(parseActionLog(saved.action_log)).toHaveLength(2);
+		expect(enqueueAppointmentReconciliation).toHaveBeenCalledExactlyOnceWith(
+			saved,
+			'edited-by-host'
+		);
+	});
+
+	test('concurrent duration and existing partial content edit both survive with one revision each', async () => {
+		await seed();
+		const ctx = context();
+		const results = await Promise.all([
+			changeAppointmentDuration(ctx, { appointmentId: baseRow.id, durationMinutes: 60 }),
+			editAppointment(ctx, {
+				appointmentId: baseRow.id,
+				note: 'Concurrent note',
+				location: 'Concurrent location'
+			})
+		]);
+		expect(results.every((result) => result.ok)).toBe(true);
+		const saved = await row();
+		expect(saved).toMatchObject({
+			note: 'Concurrent note',
+			location: 'Concurrent location',
+			end_time: '2099-01-04T16:07:00Z',
+			calendar_revision: 9,
+			ics_sequence: 6,
+			video_chat: baseRow.video_chat,
+			video_chat_request: 'generate'
+		});
+		const history = parseActionLog(saved.action_log);
+		expect(history).toHaveLength(3);
+		expect(history.slice(1).map((entry) => entry.payload?.metadata?.changes)).toEqual(
+			expect.arrayContaining([['duration_updated'], ['note_updated', 'location_updated']])
+		);
+		expect(enqueueAppointmentReconciliation).toHaveBeenCalledTimes(2);
+	});
+});
+
+describe('changeAppointmentDuration: bounded refusals', () => {
+	test('missing ID returns not_found', async () => {
+		const result = await change(60);
+		expect(result).toEqual({ ok: false, reason: 'not_found' });
+		expect(enqueueAppointmentReconciliation).not.toHaveBeenCalled();
+	});
+
+	test.each(['declined', 'cancelled', 'expired', 'rescheduled', 'purged'] as const)(
+		'gates a freshly changed %s row',
+		async (status) => {
+			await seed();
+			const page = await row();
+			await db.updateTable('appointments').set({ status }).where('id', '=', page.id).execute();
+			const before = await row();
+			const result = await change(60);
+			expect(result).toEqual({ ok: false, reason: 'gated' });
+			await expectUnwritten(before);
+		}
+	);
+
+	test.each(['2099-01-04T15:37:00Z', '2099-01-04T15:38:00Z'])(
+		'gates at/after current end (%s), even when extending',
+		async (time) => {
+			await seed();
+			now = time;
+			const before = await row();
+			const result = await change(60);
+			expect(result).toEqual({ ok: false, reason: 'gated' });
+			await expectUnwritten(before);
+		}
+	);
+
+	test('requires live meeting config, not the stored meeting snapshot, even for unchanged duration', async () => {
+		await seed();
+		delete cfg.meetings['30-min-chat'];
+		const before = await row();
+		const result = await change(30);
+		expect(result).toEqual({ ok: false, reason: 'not_configured' });
+		await expectUnwritten(before);
+	});
+
+	test.each([0, -15, 16, 85, 15.5, NaN, Infinity, -Infinity, Number.MAX_SAFE_INTEGER + 1])(
+		'rejects invalid/unoffered %s without changing the row',
+		async (duration) => {
+			await seed();
+			const before = await row();
+			const result = await change(duration);
+			expect(result).toEqual({ ok: false, reason: 'invalid_duration' });
+			await expectUnwritten(before);
+		}
+	);
+
+	test('still requires a safe integer if a malformed config happens to offer a fraction', async () => {
+		cfg.meetings['30-min-chat'].additional_duration_minutes = [22.5];
+		await seed();
+		const before = await row();
+		const result = await change(22.5);
+		expect(result).toEqual({ ok: false, reason: 'invalid_duration' });
+		await expectUnwritten(before);
+	});
+
+	test.each(['2099-01-04T15:22:00Z', '2099-01-04T15:27:00Z'])(
+		'rejects shortening to an end at/before now %s',
+		async (time) => {
+			await seed();
+			now = time;
+			const before = await row();
+			const result = await change(15);
+			expect(result).toEqual({ ok: false, reason: 'past_end' });
+			await expectUnwritten(before);
+		}
+	);
+});
+
+describe('changeAppointmentDuration: active until current end; only actual conflicts constrain host', () => {
+	test.each([
+		['pending', 30, 60],
+		['confirmed', 30, 60],
+		['pending', 60, 30],
+		['confirmed', 60, 30]
+	] as const)(
+		'allows in-progress %s, %i to %i minutes with a future new end',
+		async (status, current, duration) => {
+			await seed({
+				status,
+				end_time: Temporal.Instant.from(start).add({ minutes: current }).toString()
+			});
+			now = '2099-01-04T15:27:00Z';
+			const result = await change(duration);
+			expect(result).toMatchObject({ ok: true, outcome: 'updated' });
+			const saved = await row();
+			expect(saved).toMatchObject({
+				status,
+				start_time: start,
+				end_time: Temporal.Instant.from(start).add({ minutes: duration }).toString()
+			});
+		}
+	);
+
+	test('allows an edit exactly at the appointment start', async () => {
+		await seed();
+		now = start;
+		const result = await change(60);
+		expect(result).toMatchObject({ ok: true, outcome: 'updated' });
+	});
+
+	test.each(['2099-01-04T15:06:00Z', '2098-01-01T00:00:00Z'])(
+		'ignores working hours, off-grid start, notice, horizon, cap and padding when actually free (%s)',
+		async (time) => {
+			cfg.schedules.standard.weekly = [];
+			Object.assign(cfg.meetings['30-min-chat'], {
+				start_times_every_minutes: 60,
+				notice_minutes: 10080,
+				booking_window_days: 1,
+				daily_booking_limit: 1,
+				padding_before_minutes: 180,
+				padding_after_minutes: 180
+			});
+			now = time;
+			await seed();
+			await seed({
+				id: 'neighbour',
+				cancel_token: 'neighbour-token',
+				start_time: '2099-01-04T16:07:00Z',
+				end_time: '2099-01-04T16:37:00Z'
+			});
+			await replaceCalendarBusy(db, 'my-google-cal', [
+				{ start: '2099-01-04T14:07:00Z', end: start }
+			]);
+			const result = await change(60);
+			expect(result).toMatchObject({ ok: true, outcome: 'updated' });
+		}
+	);
+
+	test.each([
+		{
+			status: 'pending',
+			event_type_id: '30-min-chat',
+			start_time: '2099-01-04T15:50:00Z',
+			end_time: '2099-01-04T16:30:00Z'
+		},
+		{
+			status: 'confirmed',
+			event_type_id: 'different-type',
+			start_time: '2099-01-04T15:50:00Z',
+			end_time: '2099-01-04T16:30:00Z'
+		},
+		{
+			status: 'confirmed',
+			event_type_id: 'removed-type',
+			start_time: '2099-01-01T16:00:00Z',
+			end_time: '2099-01-04T16:00:00Z'
+		}
+	] as const)('refuses hard local conflict $status / $event_type_id', async (fields) => {
+		await seed();
+		await seed({ ...fields, id: 'blocker', cancel_token: 'blocker-token' });
+		const before = await row();
+		const result = await change(60);
+		expect(result).toEqual({ ok: false, reason: 'busy' });
+		await expectUnwritten(before);
+	});
+
+	test.each(['my-google-cal', 'extra'])(
+		'refuses mirrored busy in selected calendar %s',
+		async (calendar) => {
+			cfg.meetings['30-min-chat'].additional_busy_calendars = ['extra'];
+			await seed();
+			await replaceCalendarBusy(db, calendar, [
+				{ start: '2099-01-04T15:50:00Z', end: '2099-01-04T16:30:00Z' }
+			]);
+			const before = await row();
+			const result = await change(60);
+			expect(result).toEqual({ ok: false, reason: 'busy' });
+			await expectUnwritten(before);
+		}
+	);
+
+	test('shortening uses the new interval, not busy time beyond its end or unselected calendars', async () => {
+		await seed({ end_time: '2099-01-04T16:07:00Z' });
+		await replaceCalendarBusy(db, 'my-google-cal', [
+			{ start: '2099-01-04T15:37:00Z', end: '2099-01-04T16:07:00Z' }
+		]);
+		await replaceCalendarBusy(db, 'not-selected', [{ start, end: '2099-01-04T16:07:00Z' }]);
+		const result = await change(30);
+		expect(result).toMatchObject({ ok: true, outcome: 'updated' });
+	});
+});
+
+describe('changeAppointmentDuration: transaction and enqueue boundary', () => {
+	test('fresh read, actual conflict reads and update share one BEGIN IMMEDIATE before commit and enqueue', async () => {
+		await seed();
+		const rootRead = vi.spyOn(db, 'selectFrom').mockImplementation(() => {
+			throw new Error('must read on reserved connection');
+		});
+		const rootUpdate = vi.spyOn(db, 'updateTable').mockImplementation(() => {
+			throw new Error('must update on reserved connection');
+		});
+		const rootConnection = vi.spyOn(db, 'connection');
+		statements.length = 0;
+		let committedAtEnqueue: Appointment | undefined;
+		vi.mocked(enqueueAppointmentReconciliation).mockImplementationOnce(async () => {
+			expect(statements.at(-1)).toBe('COMMIT');
+			expect(rootConnection).toHaveBeenCalledTimes(1);
+			await withWriteTransaction(db, async (connection) => {
+				committedAtEnqueue = await connection
+					.selectFrom('appointments')
+					.selectAll()
+					.where('id', '=', baseRow.id)
+					.executeTakeFirstOrThrow();
+			});
+		});
+		const result = await change(60);
+		expect(result).toEqual({ ok: true, outcome: 'updated', appointment: committedAtEnqueue });
+		expect(
+			statements.slice(0, 6).map((statement) => {
+				if (statement.startsWith('update')) return 'update';
+				if (statement.includes('"external_calendar_busy"')) return 'mirror conflict read';
+				if (statement.startsWith('select "start_time"')) return 'local conflict read';
+				if (statement.startsWith('select *')) return 'fresh row read';
+				return statement;
+			})
+		).toEqual([
+			'BEGIN IMMEDIATE',
+			'fresh row read',
+			'local conflict read',
+			'mirror conflict read',
+			'update',
+			'COMMIT'
+		]);
+		expect(rootRead).not.toHaveBeenCalled();
+		expect(rootUpdate).not.toHaveBeenCalled();
+		expect(committedAtEnqueue).toMatchObject({
+			end_time: '2099-01-04T16:07:00Z',
+			calendar_revision: 8,
+			ics_sequence: 5
+		});
+	});
+
+	test('SQLite update failure escapes, rolls back and is not mislabeled as enqueue failure', async () => {
+		await seed();
+		const before = await row();
+		await sql`CREATE TRIGGER reject_duration BEFORE UPDATE ON appointments BEGIN SELECT RAISE(ABORT, 'injected duration write failure'); END`.execute(
+			db
+		);
+		const write = change(60);
+		await expect(write).rejects.toThrow('injected duration write failure');
+		await expectUnwritten(before);
+		expect(statements).toContain('ROLLBACK');
+		await sql`DROP TRIGGER reject_duration`.execute(db);
+		const retried = await change(60);
+		expect(retried).toMatchObject({ ok: true, outcome: 'updated' });
+	});
+
+	test('enqueue rejection reports the actual committed save; an unchanged retry neither reenqueues nor claims recovery', async () => {
+		await seed();
+		vi.mocked(enqueueAppointmentReconciliation).mockImplementationOnce(async () => {
+			await withWriteTransaction(db, async (connection) => {
+				const committed = await connection
+					.selectFrom('appointments')
+					.selectAll()
+					.where('id', '=', baseRow.id)
+					.executeTakeFirstOrThrow();
+				expect(committed).toMatchObject({
+					end_time: '2099-01-04T16:07:00Z',
+					calendar_revision: 8,
+					ics_sequence: 5
+				});
+			});
+			throw new Error('queue unavailable');
+		});
+		const failed = await change(60);
+		const saved = await row();
+		expect(failed).toEqual({ ok: false, reason: 'enqueue_failed', durationSaved: true });
+		expect(parseActionLog(saved.action_log)).toHaveLength(2);
+		const retry = await change(60);
+		const afterRetry = await row();
+		expect(retry).toEqual({ ok: true, outcome: 'unchanged', appointment: saved });
+		expect(afterRetry).toEqual(saved);
+		expect(enqueueAppointmentReconciliation).toHaveBeenCalledExactlyOnceWith(
+			saved,
+			'edited-by-host'
+		);
+	});
+});
diff --git a/apps/web/src/lib/server/appointment/change-duration.ts b/apps/web/src/lib/server/appointment/change-duration.ts
new file mode 100644
index 00000000..3ac5929b
--- /dev/null
+++ b/apps/web/src/lib/server/appointment/change-duration.ts
@@ -0,0 +1,87 @@
+import { sql } from 'kysely';
+import {
+	appendActionLogSql,
+	findAppointment,
+	withWriteTransaction,
+	type Appointment
+} from '@when/db';
+import { isEditAllowed } from './access';
+import { resolveBookingDurations } from './duration';
+import type { AppointmentContext } from './context';
+import { hasAppointmentConflict } from '../availability/conflicts';
+import { enqueueAppointmentReconciliation } from '../workflow';
+
+export type ChangeDurationResult =
+	| { ok: true; outcome: 'updated' | 'unchanged'; appointment: Appointment }
+	| {
+			ok: false;
+			reason: 'not_found' | 'gated' | 'not_configured' | 'invalid_duration' | 'past_end' | 'busy';
+	  }
+	| { ok: false; reason: 'enqueue_failed'; durationSaved: true };
+
+export async function changeAppointmentDuration(
+	ctx: AppointmentContext,
+	input: { appointmentId: string; durationMinutes: number }
+): Promise<ChangeDurationResult> {
+	const committed = await withWriteTransaction(ctx.db, async (connection) => {
+		const appointment = await findAppointment(connection, input.appointmentId);
+		if (!appointment) return { ok: false, reason: 'not_found' } as const;
+		const now = ctx.clock.now();
+		if (!isEditAllowed(appointment, now)) {
+			return { ok: false, reason: 'gated' } as const;
+		}
+
+		const meeting = ctx.cfg.meetings[appointment.event_type_id];
+		if (!meeting) return { ok: false, reason: 'not_configured' } as const;
+		const profile = resolveBookingDurations(meeting, 'host', appointment);
+		if (
+			!Number.isSafeInteger(input.durationMinutes) ||
+			!profile.durations.includes(input.durationMinutes)
+		) {
+			return { ok: false, reason: 'invalid_duration' } as const;
+		}
+		if (input.durationMinutes === profile.defaultDuration) {
+			return { ok: true, outcome: 'unchanged', appointment } as const;
+		}
+
+		const start = Temporal.Instant.from(appointment.start_time);
+		const end = start.add({ minutes: input.durationMinutes });
+		if (end.epochMilliseconds <= now.getTime()) return { ok: false, reason: 'past_end' } as const;
+		const busy = await hasAppointmentConflict(connection, meeting, { start, end }, appointment.id);
+		if (busy) return { ok: false, reason: 'busy' } as const;
+
+		const updated = await connection
+			.updateTable('appointments')
+			.set({
+				end_time: end.toString(),
+				calendar_revision: sql`calendar_revision + 1`,
+				ics_sequence: sql`ics_sequence + 1`,
+				updated_at: sql`CURRENT_TIMESTAMP`,
+				action_log: appendActionLogSql({
+					action: 'edit',
+					actor: 'host',
+					at: now.toISOString(),
+					payload: {
+						metadata: {
+							changes: ['duration_updated'],
+							previous_duration: profile.defaultDuration,
+							duration: input.durationMinutes
+						}
+					}
+				})
+			})
+			.where('id', '=', appointment.id)
+			.where('status', 'in', ['pending', 'confirmed'])
+			.returningAll()
+			.executeTakeFirstOrThrow();
+		return { ok: true, outcome: 'updated', appointment: updated } as const;
+	});
+	if (!committed.ok || committed.outcome === 'unchanged') return committed;
+
+	try {
+		await enqueueAppointmentReconciliation(committed.appointment, 'edited-by-host');
+	} catch {
+		return { ok: false, reason: 'enqueue_failed', durationSaved: true };
+	}
+	return committed;
+}
diff --git a/apps/web/src/lib/server/appointment/duration-reschedule-race.test.ts b/apps/web/src/lib/server/appointment/duration-reschedule-race.test.ts
new file mode 100644
index 00000000..aba03630
--- /dev/null
+++ b/apps/web/src/lib/server/appointment/duration-reschedule-race.test.ts
@@ -0,0 +1,219 @@
+import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
+import { openDb, parseActionLog, runMigrations, type Appointment } from '@when/db';
+import { validConfig } from '$lib/server/__fixtures__/valid-config';
+import { changeAppointmentDuration } from './change-duration';
+import { resolveDuration } from './duration';
+import { rescheduleAppointment, type RescheduleAppointmentInput } from './reschedule';
+import type { AppointmentContext } from './context';
+import type { AppointmentRole } from './actions';
+
+vi.mock('../workflow', () => ({ enqueueAppointmentReconciliation: vi.fn() }));
+import { enqueueAppointmentReconciliation } from '../workflow';
+
+const appointmentId = 'duration-race';
+const now = new Date('2099-01-01T12:00:00Z');
+const newStart = '2099-01-06T10:00:00Z';
+const initialHistory = [{ action: 'create', actor: 'guest', at: '2098-12-01T12:00:00Z' }];
+let db: ReturnType<typeof openDb>;
+let ctx: AppointmentContext;
+
+async function currentRow() {
+	const row = await db
+		.selectFrom('appointments')
+		.selectAll()
+		.where('id', '=', appointmentId)
+		.executeTakeFirstOrThrow();
+	return row;
+}
+
+function prevalidate(
+	row: Appointment,
+	role: AppointmentRole,
+	duration: number
+): RescheduleAppointmentInput {
+	const form = new FormData();
+	form.set('duration', String(duration));
+	const resolved = resolveDuration(ctx.cfg.meetings[row.event_type_id], role, form, row);
+	expect(resolved).toBe(duration);
+	return {
+		appointmentId: row.id,
+		initiator: role,
+		newStart,
+		newEnd: Temporal.Instant.from(newStart).add({ minutes: duration }).toString()
+	};
+}
+
+beforeEach(async () => {
+	db = openDb(':memory:');
+	await runMigrations(db);
+	const cfg = structuredClone(validConfig);
+	cfg.meetings['30-min-chat'].duration_minutes = 30;
+	cfg.meetings['30-min-chat'].additional_duration_minutes = [];
+	ctx = { db, cfg, clock: { now: () => now, nowMs: () => now.getTime() } };
+	await db
+		.insertInto('appointments')
+		.values({
+			id: appointmentId,
+			event_type_id: '30-min-chat',
+			start_time: '2099-01-05T10:00:00Z',
+			end_time: '2099-01-05T11:30:00Z',
+			status: 'confirmed',
+			origin_id: appointmentId,
+			cancel_token: 'original-token',
+			guest_name: 'Guest',
+			guest_email: 'guest@example.com',
+			location: 'Existing location',
+			note: 'Existing host note',
+			video_chat: 'https://video.example/keep',
+			video_chat_request: 'suppress',
+			external_event_id: 'published-event',
+			external_calendar_id: 'my-google-cal',
+			action_log: JSON.stringify(initialHistory)
+		})
+		.execute();
+	vi.mocked(enqueueAppointmentReconciliation).mockReset();
+	vi.mocked(enqueueAppointmentReconciliation).mockResolvedValue(undefined);
+});
+
+afterEach(async () => {
+	await db.destroy();
+});
+
+describe('duration change between reschedule prevalidation and commit', () => {
+	test('gates a guest request retaining stale 90 minutes after the host commits 60 minutes', async () => {
+		const page = await currentRow();
+		const request = prevalidate(page, 'guest', 90);
+
+		const changed = await changeAppointmentDuration(ctx, { appointmentId, durationMinutes: 60 });
+		const committed = await currentRow();
+		expect(changed).toEqual({ ok: true, outcome: 'updated', appointment: committed });
+		expect(committed).toMatchObject({
+			status: 'confirmed',
+			start_time: page.start_time,
+			end_time: '2099-01-05T11:00:00Z',
+			calendar_revision: 1,
+			ics_sequence: 1
+		});
+		expect(enqueueAppointmentReconciliation).toHaveBeenCalledExactlyOnceWith(
+			committed,
+			'edited-by-host'
+		);
+
+		const result = await rescheduleAppointment(ctx, request);
+		const rows = await db.selectFrom('appointments').selectAll().execute();
+		expect(result).toEqual({ ok: false, reason: 'gated' });
+		expect(rows).toEqual([committed]);
+		expect(parseActionLog(rows[0].action_log)).toEqual([
+			...initialHistory,
+			{
+				action: 'edit',
+				actor: 'host',
+				at: now.toISOString(),
+				payload: {
+					metadata: { changes: ['duration_updated'], previous_duration: 90, duration: 60 }
+				}
+			}
+		]);
+		expect(enqueueAppointmentReconciliation).toHaveBeenCalledExactlyOnceWith(
+			committed,
+			'edited-by-host'
+		);
+	});
+
+	test.each([
+		{
+			name: 'guest requested configured 30 before the host change',
+			role: 'guest',
+			savedDuration: 60,
+			requestedDuration: 30,
+			validateFresh: false
+		},
+		{
+			name: 'guest retains fresh 60 after the host change',
+			role: 'guest',
+			savedDuration: 60,
+			requestedDuration: 60,
+			validateFresh: true
+		},
+		{
+			name: 'guest retains unchanged original 90',
+			role: 'guest',
+			savedDuration: 90,
+			requestedDuration: 90,
+			validateFresh: false
+		},
+		{
+			name: 'host still chooses host-only 90 after saving 60',
+			role: 'host',
+			savedDuration: 60,
+			requestedDuration: 90,
+			validateFresh: false
+		}
+	] as const)(
+		'$name remains allowed',
+		async ({ role, savedDuration, requestedDuration, validateFresh }) => {
+			const page = await currentRow();
+			let request = validateFresh ? undefined : prevalidate(page, role, requestedDuration);
+			const changed = await changeAppointmentDuration(ctx, {
+				appointmentId,
+				durationMinutes: savedDuration
+			});
+			const committed = await currentRow();
+			const durationChanged = savedDuration !== 90;
+			expect(changed).toEqual({
+				ok: true,
+				outcome: durationChanged ? 'updated' : 'unchanged',
+				appointment: committed
+			});
+			if (validateFresh) request = prevalidate(committed, role, requestedDuration);
+			if (!request) throw new Error('control request was not prevalidated');
+
+			const result = await rescheduleAppointment(ctx, request);
+			expect(result.ok).toBe(true);
+			if (!result.ok) throw new Error(`control reschedule refused: ${result.reason}`);
+			const rows = await db.selectFrom('appointments').selectAll().execute();
+			const original = rows.find((row) => row.id === appointmentId);
+			const successor = rows.find((row) => row.id === result.appointment.id);
+			expect(rows).toHaveLength(2);
+			expect(successor).toEqual(result.appointment);
+			expect(result.appointment.id).not.toBe(appointmentId);
+			expect(result.appointment).toMatchObject({
+				status: 'confirmed',
+				origin_id: appointmentId,
+				start_time: newStart,
+				end_time: request.newEnd,
+				note: committed.note,
+				video_chat: committed.video_chat,
+				video_chat_request: committed.video_chat_request,
+				ics_sequence: committed.ics_sequence + 1
+			});
+			expect(original).toMatchObject({
+				status: 'rescheduled',
+				start_time: page.start_time,
+				end_time: committed.end_time,
+				calendar_revision: committed.calendar_revision,
+				ics_sequence: committed.ics_sequence
+			});
+			const history = parseActionLog(result.appointment.action_log);
+			expect(history.slice(0, -1)).toEqual(parseActionLog(committed.action_log));
+			expect(history.at(-1)).toMatchObject({
+				action: 'reschedule',
+				actor: role,
+				payload: { metadata: { previous_id: appointmentId, next_id: result.appointment.id } }
+			});
+			expect(original?.action_log).toBe(result.appointment.action_log);
+			expect(enqueueAppointmentReconciliation).toHaveBeenCalledTimes(durationChanged ? 2 : 1);
+			if (durationChanged) {
+				expect(enqueueAppointmentReconciliation).toHaveBeenNthCalledWith(
+					1,
+					committed,
+					'edited-by-host'
+				);
+			}
+			expect(enqueueAppointmentReconciliation).toHaveBeenLastCalledWith(
+				result.appointment,
+				`rescheduled-by-${role}`
+			);
+		}
+	);
+});
diff --git a/apps/web/src/lib/server/appointment/reschedule.ts b/apps/web/src/lib/server/appointment/reschedule.ts
index fcdd045e..2bc97266 100644
--- a/apps/web/src/lib/server/appointment/reschedule.ts
+++ b/apps/web/src/lib/server/appointment/reschedule.ts
@@ -1,5 +1,6 @@
 import { resolveAppointmentActions, isTerminalStatus, type AppointmentRole } from './actions';
 import { isRescheduleAllowed, isViewable } from './access';
+import { resolveBookingDurations } from './duration';
 import { enqueueAppointmentReconciliation } from '../workflow';
 import type { AppointmentContext } from './context';
 import {
@@ -72,6 +73,12 @@ export async function rescheduleAppointment(
 				eventType
 			}).reschedule;
 			if (!gate.allowed) return { ok: false, reason: 'gated' } as const;
+			// A concurrent duration edit can revoke the old booked-length exception.
+			if (eventType) {
+				const duration = (Date.parse(input.newEnd) - Date.parse(input.newStart)) / 60_000;
+				const profile = resolveBookingDurations(eventType, input.initiator, appointment);
+				if (!profile.durations.includes(duration)) return { ok: false, reason: 'gated' } as const;
+			}
 
 			const details = rescheduleDetails(appointment, input, eventType);
 			const moved = await rescheduleAppointmentTransition(
diff --git a/apps/web/src/lib/server/availability/conflicts.test.ts b/apps/web/src/lib/server/availability/conflicts.test.ts
new file mode 100644
index 00000000..a82916b5
--- /dev/null
+++ b/apps/web/src/lib/server/availability/conflicts.test.ts
@@ -0,0 +1,211 @@
+import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
+import {
+	openDb,
+	replaceCalendarBusy,
+	runMigrations,
+	withWriteTransaction,
+	type NewAppointment
+} from '@when/db';
+import { validConfig } from '$lib/server/__fixtures__/valid-config';
+import { hasAppointmentConflict } from './conflicts';
+
+const meeting = {
+	...validConfig.meetings['30-min-chat'],
+	booking_calendar: 'booking',
+	additional_busy_calendars: ['extra', 'booking', 'extra']
+};
+const interval = {
+	start: Temporal.Instant.from('2099-01-04T15:07:00Z'),
+	end: Temporal.Instant.from('2099-01-04T16:07:00Z')
+};
+
+let db: ReturnType<typeof openDb>;
+
+async function seed(changes: Partial<NewAppointment> = {}) {
+	await db
+		.insertInto('appointments')
+		.values({
+			id: 'other',
+			event_type_id: '30-min-chat',
+			start_time: '2099-01-04T15:45:00Z',
+			end_time: '2099-01-04T16:30:00Z',
+			guest_name: 'Guest',
+			status: 'confirmed',
+			cancel_token: 'other-token',
+			location: null,
+			note: null,
+			video_chat: null,
+			external_event_id: null,
+			external_calendar_id: null,
+			...changes
+		})
+		.execute();
+}
+
+beforeEach(async () => {
+	db = openDb(':memory:');
+	await runMigrations(db);
+});
+
+afterEach(async () => {
+	vi.restoreAllMocks();
+	await db.destroy();
+});
+
+describe('hasAppointmentConflict: local actual intervals', () => {
+	test.each(['pending', 'confirmed'] as const)('blocks an overlapping %s row', async (status) => {
+		await seed({ status });
+		const busy = await hasAppointmentConflict(db, meeting, interval, 'self');
+		expect(busy).toBe(true);
+	});
+
+	test('blocks other meeting types, even one no longer configured', async () => {
+		await seed({ event_type_id: 'removed-meeting' });
+		const busy = await hasAppointmentConflict(db, meeting, interval, 'self');
+		expect(busy).toBe(true);
+	});
+
+	test('includes a three-day appointment starting far before the candidate day', async () => {
+		await seed({ start_time: '2099-01-01T16:00:00Z', end_time: '2099-01-04T16:00:00Z' });
+		const busy = await hasAppointmentConflict(db, meeting, interval, 'self');
+		expect(busy).toBe(true);
+	});
+
+	test.each(['declined', 'cancelled', 'expired', 'rescheduled', 'purged'] as const)(
+		'ignores overlapping inactive status %s',
+		async (status) => {
+			await seed({ status });
+			const busy = await hasAppointmentConflict(db, meeting, interval, 'self');
+			expect(busy).toBe(false);
+		}
+	);
+
+	test('excludes only the supplied appointment ID, not all rows of its type', async () => {
+		await seed({ id: 'self', cancel_token: 'self-token' });
+		const selfOnly = await hasAppointmentConflict(db, meeting, interval, 'self');
+		expect(selfOnly).toBe(false);
+		await seed({ start_time: '2099-01-04T15:50:00Z' });
+		const otherRow = await hasAppointmentConflict(db, meeting, interval, 'self');
+		expect(otherRow).toBe(true);
+	});
+
+	test.each([
+		['ends at candidate start', '2099-01-04T14:00:00Z', '2099-01-04T15:07:00Z'],
+		['starts at candidate end', '2099-01-04T16:07:00Z', '2099-01-04T17:00:00Z'],
+		['is earlier', '2099-01-04T13:00:00Z', '2099-01-04T14:00:00Z'],
+		['is later', '2099-01-04T17:00:00Z', '2099-01-04T18:00:00Z']
+	])('allows a local row that %s', async (_name, start_time, end_time) => {
+		await seed({ start_time, end_time });
+		const busy = await hasAppointmentConflict(db, meeting, interval, 'self');
+		expect(busy).toBe(false);
+	});
+});
+
+describe('hasAppointmentConflict: local remote-busy mirror', () => {
+	test.each(['booking', 'extra'])(
+		'blocks actual busy time in the %s calendar',
+		async (calendar) => {
+			await replaceCalendarBusy(db, calendar, [
+				{ start: '2099-01-04T16:00:00Z', end: '2099-01-04T17:00:00Z' }
+			]);
+			const busy = await hasAppointmentConflict(db, meeting, interval, 'self');
+			expect(busy).toBe(true);
+		}
+	);
+
+	test('ignores a busy calendar not selected by the supplied meeting', async () => {
+		await replaceCalendarBusy(db, 'unselected', [
+			{ start: interval.start.toString(), end: interval.end.toString() }
+		]);
+		const free = await hasAppointmentConflict(db, meeting, interval, 'self');
+		expect(free).toBe(false);
+		const selectedMeeting = { ...meeting, additional_busy_calendars: ['unselected'] };
+		const busy = await hasAppointmentConflict(db, selectedMeeting, interval, 'self');
+		expect(busy).toBe(true);
+	});
+
+	test.each([
+		['ends at start', '2099-01-04T14:00:00Z', '2099-01-04T15:07:00Z'],
+		['starts at end', '2099-01-04T16:07:00Z', '2099-01-04T17:00:00Z'],
+		['outside the window', '2099-01-05T15:00:00Z', '2099-01-05T16:00:00Z']
+	])('allows mirrored busy time that %s', async (_name, start, end) => {
+		await replaceCalendarBusy(db, 'booking', [{ start, end }]);
+		const busy = await hasAppointmentConflict(db, meeting, interval, 'self');
+		expect(busy).toBe(false);
+	});
+
+	test('uses the supplied actual interval, not the configured default duration', async () => {
+		await replaceCalendarBusy(db, 'booking', [
+			{ start: '2099-01-04T16:30:00Z', end: '2099-01-04T17:00:00Z' }
+		]);
+		const short = await hasAppointmentConflict(db, meeting, interval, 'self');
+		const extended = await hasAppointmentConflict(
+			db,
+			meeting,
+			{ ...interval, end: interval.start.add({ minutes: 120 }) },
+			'self'
+		);
+		expect(short).toBe(false);
+		expect(extended).toBe(true);
+	});
+
+	test('reads a replacement mirror without fetching a provider', async () => {
+		await replaceCalendarBusy(db, 'booking', [
+			{ start: interval.start.toString(), end: interval.end.toString() }
+		]);
+		const before = await hasAppointmentConflict(db, meeting, interval, 'self');
+		await replaceCalendarBusy(db, 'booking', []);
+		const after = await hasAppointmentConflict(db, meeting, interval, 'self');
+		expect(before).toBe(true);
+		expect(after).toBe(false);
+	});
+});
+
+test('uses the supplied write connection for both local and mirror reads without reacquiring root', async () => {
+	await replaceCalendarBusy(db, 'booking', [
+		{ start: interval.start.toString(), end: interval.end.toString() }
+	]);
+	const rootRead = vi.spyOn(db, 'selectFrom');
+	const rootConnection = vi.spyOn(db, 'connection');
+	await withWriteTransaction(db, async (connection) => {
+		rootRead.mockImplementation(() => {
+			throw new Error('root read inside reserved connection');
+		});
+		rootConnection.mockImplementation(() => {
+			throw new Error('root connection reacquired');
+		});
+		const busy = await hasAppointmentConflict(connection, meeting, interval, 'self');
+		expect(busy).toBe(true);
+	});
+	expect(rootRead).not.toHaveBeenCalled();
+	expect(rootConnection).toHaveBeenCalledTimes(1);
+});
+
+test('sees an uncommitted local row on the supplied connection', async () => {
+	const rollback = new Error('discard fixture write');
+	const write = withWriteTransaction(db, async (connection) => {
+		await connection
+			.insertInto('appointments')
+			.values({
+				id: 'inside',
+				event_type_id: 'another-type',
+				status: 'pending',
+				cancel_token: 'inside-token',
+				start_time: interval.start.toString(),
+				end_time: interval.end.toString(),
+				guest_name: 'Guest',
+				location: null,
+				note: null,
+				video_chat: null,
+				external_event_id: null,
+				external_calendar_id: null
+			})
+			.execute();
+		const busy = await hasAppointmentConflict(connection, meeting, interval, 'self');
+		expect(busy).toBe(true);
+		throw rollback;
+	});
+	await expect(write).rejects.toBe(rollback);
+	const afterRollback = await hasAppointmentConflict(db, meeting, interval, 'self');
+	expect(afterRollback).toBe(false);
+});
diff --git a/apps/web/src/lib/server/availability/conflicts.ts b/apps/web/src/lib/server/availability/conflicts.ts
new file mode 100644
index 00000000..70211bba
--- /dev/null
+++ b/apps/web/src/lib/server/availability/conflicts.ts
@@ -0,0 +1,36 @@
+import type { Kysely } from 'kysely';
+import { getBusyIntervals, type Database } from '@when/db';
+import { busyCalendarsFor } from '@when/calendar';
+import type { Meeting } from '@when/config';
+import { overlapsAny } from './intervals';
+import type { Interval } from './types';
+
+export async function hasAppointmentConflict(
+	db: Kysely<Database>,
+	meeting: Meeting,
+	interval: Interval,
+	excludeAppointmentId: string
+): Promise<boolean> {
+	// A long appointment can overlap this interval even if it started much earlier.
+	const local = await db
+		.selectFrom('appointments')
+		.select(['start_time', 'end_time'])
+		.where('status', 'in', ['pending', 'confirmed'])
+		.where('id', '!=', excludeAppointmentId)
+		.execute();
+	const localIntervals = local.map((row) => ({
+		start: Temporal.Instant.from(row.start_time),
+		end: Temporal.Instant.from(row.end_time)
+	}));
+	if (overlapsAny(interval, localIntervals)) return true;
+
+	const remote = await getBusyIntervals(db, busyCalendarsFor(meeting), {
+		start: interval.start.toString(),
+		end: interval.end.toString()
+	});
+	const remoteIntervals = remote.map((row) => ({
+		start: Temporal.Instant.from(row.start),
+		end: Temporal.Instant.from(row.end)
+	}));
+	return overlapsAny(interval, remoteIntervals);
+}
diff --git a/apps/web/src/routes/(app)/appointment/[id]/+page.server.ts b/apps/web/src/routes/(app)/appointment/[id]/+page.server.ts
index 22f9690e..9c77de84 100644
--- a/apps/web/src/routes/(app)/appointment/[id]/+page.server.ts
+++ b/apps/web/src/routes/(app)/appointment/[id]/+page.server.ts
@@ -1,6 +1,6 @@
 import { error, fail, redirect } from '@sveltejs/kit';
 import { shouldAttachVideoChat } from '@when/video-chat';
-import { isViewAllowed } from '$lib/server/appointment/access';
+import { isEditAllowed, isViewAllowed } from '$lib/server/appointment/access';
 import {
 	isActiveStatus,
 	resolveAppointmentActions,
@@ -140,6 +140,7 @@ export const load: PageServerLoad = async ({ params, url, locals, cookies }) =>
 		appointment,
 		videoChatRequested,
 		eventType: toPublicEventType(row.event_type_id, resolvedEventType, role, bookingDurations),
+		canEditDuration: isHost && Boolean(eventType) && isEditAllowed(row, now),
 		calendarLinks,
 		actions,
 		flash: flash ?? null,
diff --git a/apps/web/src/routes/(app)/appointment/[id]/+page.svelte b/apps/web/src/routes/(app)/appointment/[id]/+page.svelte
index 75a8d94a..ffa59fa0 100644
--- a/apps/web/src/routes/(app)/appointment/[id]/+page.svelte
+++ b/apps/web/src/routes/(app)/appointment/[id]/+page.svelte
@@ -13,6 +13,7 @@
 	import IconPencilSimple from 'virtual:icons/ph/pencil-simple';
 	import IconVideo from 'virtual:icons/ph/video-conference';
 	import AppointmentActions from '$lib/components/AppointmentActions.svelte';
+	import DurationEditor from '$lib/components/DurationEditor.svelte';
 	import AppointmentLog from '$lib/components/AppointmentLog.svelte';
 	import AppointmentQuestions from '$lib/components/AppointmentQuestions.svelte';
 	import AddToCalendar from '$lib/components/AddToCalendar.svelte';
@@ -26,6 +27,7 @@
 	let editNoteDialogOpen = $state(false);
 	let editLocationDialogOpen = $state(false);
 	let editVideoChatDialogOpen = $state(false);
+	let editDurationDialogOpen = $state(false);
 	let changingVideoChat = $state(false);
 	let videoChatError = $state<{ message?: string } | null>(null);
 	let cancelReason = $state('I can no longer attend');
@@ -311,6 +313,7 @@
 					onGenerateVideoChat={handleGenerateVideoChat}
 					onRemoveVideoChat={handleRemoveVideoChat}
 					onEditVideoChat={() => (editVideoChatDialogOpen = true)}
+					onEditDuration={data.canEditDuration ? () => (editDurationDialogOpen = true) : undefined}
 					{isEditable}
 				/>
 			{/if}
@@ -572,6 +575,15 @@
 	{/if}
 </main>
 
+{#if data.canEditDuration}
+	<DurationEditor
+		bind:open={editDurationDialogOpen}
+		appointmentId={data.appointment.id}
+		currentDuration={data.eventType.duration_minutes}
+		durations={data.eventType.durations}
+	/>
+{/if}
+
 <Dialog.Root bind:open={cancelDialogOpen}>
 	<Dialog.Portal>
 		<Dialog.Overlay>
diff --git a/apps/web/src/routes/(app)/appointment/[id]/server.test.ts b/apps/web/src/routes/(app)/appointment/[id]/server.test.ts
index b4d181b4..59e913b0 100644
--- a/apps/web/src/routes/(app)/appointment/[id]/server.test.ts
+++ b/apps/web/src/routes/(app)/appointment/[id]/server.test.ts
@@ -143,6 +143,14 @@ vi.mock('@when/db', async (importOriginal) => {
 					note: 'Private prep',
 					video_chat: 'Private video'
 				};
+			if (id === 'appt-pending-ended')
+				return {
+					...mockAppt,
+					id,
+					status: 'pending',
+					start_time: '2000-01-01T15:00:00Z',
+					end_time: '2000-01-01T15:30:00Z'
+				};
 			if (id === 'appt-auto-video') return { ...automaticVideoAppointment, id };
 			if (id === 'appt-auto-phone')
 				return {
@@ -212,6 +220,9 @@ describe('/appointment/[id] server load', () => {
 				role === 'guest' ? row.cancel_token : null,
 				role
 			);
+			expect(result.canEditDuration).toBe(role === 'host');
+			expect(result).not.toHaveProperty('meetingConfigured');
+			expect(result.role).toBe(role);
 			expect(resolveBookingDurations).toHaveBeenCalledExactlyOnceWith(meeting, role, row);
 			expect(vi.mocked(resolveBookingDurations).mock.calls[0][2]).toBe(row);
 			const bookingDurations = vi.mocked(resolveBookingDurations).mock.results[0].value;
@@ -233,6 +244,7 @@ describe('/appointment/[id] server load', () => {
 		async (role) => {
 			const result = await loadAppointment('appt-pending', 'tok-abc', role);
 			expect(result.role).toBe(role);
+			expect(result.canEditDuration).toBe(role === 'host');
 			expect(result).not.toHaveProperty('viewer');
 			expect(result).not.toHaveProperty('isAdmin');
 			expect(result).not.toHaveProperty('isHost');
@@ -244,6 +256,15 @@ describe('/appointment/[id] server load', () => {
 		}
 	);
 
+	test('does not allow the host to edit the duration of an ended pending appointment', async () => {
+		const result = await loadAppointment('appt-pending-ended', null, 'host');
+
+		expect(result.role).toBe('host');
+		expect(result.appointment.status).toBe('pending');
+		expect(result.clockStatus).toBe('concluded');
+		expect(result.canEditDuration).toBe(false);
+	});
+
 	test('renders successfully for guest when event type is active', async () => {
 		const mockLocals = {
 			auth: vi.fn().mockResolvedValue(null)
diff --git a/apps/web/src/routes/(auth)/admin/appointment/[id]/+page.server.ts b/apps/web/src/routes/(auth)/admin/appointment/[id]/+page.server.ts
index 6b832693..822ce616 100644
--- a/apps/web/src/routes/(auth)/admin/appointment/[id]/+page.server.ts
+++ b/apps/web/src/routes/(auth)/admin/appointment/[id]/+page.server.ts
@@ -6,6 +6,7 @@ import { declineAppointment } from '$lib/server/appointment/decline';
 import { cancelAppointment } from '$lib/server/appointment/cancel';
 import { purgeAppointment } from '$lib/server/appointment/purge';
 import { editAppointment } from '$lib/server/appointment/edit';
+import { changeAppointmentDuration } from '$lib/server/appointment/change-duration';
 import { validateReason } from '$lib/server/appointment/form.server';
 import { appointmentContext } from '$lib/server/appointment/context';
 import { rotateGuestTokenTransition } from '$lib/server/appointment/transitions';
@@ -142,6 +143,46 @@ export const actions: Actions = {
 		return { success: 'edited' };
 	},
 
+	changeDuration: async ({ params, request }) => {
+		const form = await request.formData();
+		const value = form.get('duration');
+		if (typeof value !== 'string' || !value.trim()) {
+			return fail(400, { error: 'Please pick a valid meeting length.' });
+		}
+		const durationMinutes = Number(value);
+		if (!Number.isSafeInteger(durationMinutes) || durationMinutes <= 0) {
+			return fail(400, { error: 'Please pick a valid meeting length.' });
+		}
+		const result = await changeAppointmentDuration(appointmentContext(), {
+			appointmentId: params.id,
+			durationMinutes
+		});
+		if (!result.ok) {
+			switch (result.reason) {
+				case 'not_found':
+					return fail(404, { error: 'Appointment not found.' });
+				case 'not_configured':
+					return fail(409, { error: 'This meeting type no longer exists.' });
+				case 'invalid_duration':
+					return fail(400, { error: 'Please pick a valid meeting length.' });
+				case 'past_end':
+					return fail(400, { error: 'Choose a length that ends in the future.' });
+				case 'gated':
+					return fail(400, { error: 'This appointment cannot be edited.' });
+				case 'busy':
+					return fail(409, { error: 'That length overlaps another appointment or busy event.' });
+				case 'enqueue_failed':
+					return fail(500, {
+						error:
+							'The duration was saved, but calendar and email update submission could not be confirmed.',
+						durationSaved: true
+					});
+			}
+		}
+		if (result.outcome === 'unchanged') return { success: 'no_change' };
+		return { success: 'duration_changed' };
+	},
+
 	generateVideoChat: async ({ params }) => {
 		const result = await requestVideoChat(appointmentContext(), { appointmentId: params.id });
 		if (!result.ok) {
diff --git a/apps/web/src/routes/(auth)/admin/appointment/[id]/server.test.ts b/apps/web/src/routes/(auth)/admin/appointment/[id]/server.test.ts
index 12f8d96e..4db3d5d2 100644
--- a/apps/web/src/routes/(auth)/admin/appointment/[id]/server.test.ts
+++ b/apps/web/src/routes/(auth)/admin/appointment/[id]/server.test.ts
@@ -1,16 +1,23 @@
 import { describe, expect, test, vi, beforeEach } from 'vitest';
 import { actions, load } from './+page.server';
 import { requestVideoChat } from '$lib/server/appointment/request-video-chat';
+import { changeAppointmentDuration } from '$lib/server/appointment/change-duration';
+import type { Appointment } from '@when/db';
 import type { RequestEvent } from './$types';
 
 vi.mock('$lib/server/appointment/context', () => ({ appointmentContext: () => context }));
 vi.mock('$lib/server/appointment/request-video-chat', () => ({ requestVideoChat: vi.fn() }));
+vi.mock('$lib/server/appointment/change-duration', async (importOriginal) => {
+	const original = await importOriginal<typeof import('$lib/server/appointment/change-duration')>();
+	return { ...original, changeAppointmentDuration: vi.fn() };
+});
 
 const context = { db: {}, cfg: {}, clock: {} };
 const event = { params: { id: 'appt-1' } } as unknown as RequestEvent;
 
 beforeEach(() => {
 	vi.mocked(requestVideoChat).mockReset();
+	vi.mocked(changeAppointmentDuration).mockReset();
 });
 
 describe('admin appointment load', () => {
@@ -72,3 +79,131 @@ describe('generateVideoChat action', () => {
 		});
 	});
 });
+
+describe('changeDuration action', () => {
+	function changeDurationWith(form: FormData) {
+		return actions.changeDuration({
+			params: { id: 'appt-1' },
+			request: new Request('http://localhost', { method: 'POST', body: form })
+		} as unknown as RequestEvent);
+	}
+
+	test.each(['updated', 'unchanged'] as const)(
+		'maps %s while passing only the route id and parsed duration to the fresh-row service',
+		async (outcome) => {
+			// The route does not consume the service's returned row.
+			const appointment = { id: 'fresh-service-row' } as Appointment;
+			vi.mocked(changeAppointmentDuration).mockResolvedValue({ ok: true, outcome, appointment });
+			const form = new FormData();
+			form.set('duration', ' 60 ');
+			for (const [key, value] of Object.entries({
+				id: 'forged-id',
+				appointmentId: 'forged-id',
+				start: '2000-01-01T00:00:00Z',
+				start_time: '2000-01-01T00:00:00Z',
+				end_time: '2099-01-01T00:00:00Z',
+				role: 'guest',
+				viewer: 'host',
+				isAdmin: 'true',
+				isHost: 'true',
+				event_type_id: 'forged-meeting',
+				durationMinutes: '300',
+				note: 'forged note',
+				location: 'forged location',
+				video_chat: 'https://forged.example.test'
+			})) {
+				form.set(key, value);
+			}
+
+			const result = await changeDurationWith(form);
+
+			expect(changeAppointmentDuration).toHaveBeenCalledExactlyOnceWith(context, {
+				appointmentId: 'appt-1',
+				durationMinutes: 60
+			});
+			expect(result).toEqual({
+				success: outcome === 'unchanged' ? 'no_change' : 'duration_changed'
+			});
+		}
+	);
+
+	test.each([
+		['missing', null],
+		['empty', ''],
+		['whitespace', '   '],
+		['file', new File(['60'], 'duration.txt')],
+		['fractional', '1.5'],
+		['zero', '0'],
+		['negative', '-15'],
+		['NaN', 'NaN'],
+		['infinity', 'Infinity'],
+		['negative infinity', '-Infinity'],
+		['overflow', '1e309'],
+		['unsafe integer', '9007199254740992'],
+		['nonnumeric', 'sixty']
+	] as const)('rejects %s duration before calling the service', async (_label, value) => {
+		const form = new FormData();
+		if (value !== null) form.set('duration', value);
+
+		const result = await changeDurationWith(form);
+
+		expect(result).toEqual({
+			status: 400,
+			data: { error: 'Please pick a valid meeting length.' }
+		});
+		expect(result).not.toHaveProperty('success');
+		expect(changeAppointmentDuration).not.toHaveBeenCalled();
+	});
+
+	test.each([
+		['not_found', 404, 'Appointment not found.'],
+		['not_configured', 409, 'This meeting type no longer exists.'],
+		['invalid_duration', 400, 'Please pick a valid meeting length.'],
+		['past_end', 400, 'Choose a length that ends in the future.'],
+		['gated', 400, 'This appointment cannot be edited.'],
+		['busy', 409, 'That length overlaps another appointment or busy event.']
+	] as const)(
+		'maps %s without claiming success or a saved duration',
+		async (reason, status, error) => {
+			vi.mocked(changeAppointmentDuration).mockResolvedValue({ ok: false, reason });
+			const form = new FormData();
+			form.set('duration', '60');
+
+			const result = await changeDurationWith(form);
+
+			expect(changeAppointmentDuration).toHaveBeenCalledExactlyOnceWith(context, {
+				appointmentId: 'appt-1',
+				durationMinutes: 60
+			});
+			expect(result).toEqual({ status, data: { error } });
+			expect(result).not.toHaveProperty('success');
+			expect(result).not.toHaveProperty('data.durationSaved');
+		}
+	);
+
+	test('reports the saved duration but unconfirmed update submission on enqueue failure', async () => {
+		vi.mocked(changeAppointmentDuration).mockResolvedValue({
+			ok: false,
+			reason: 'enqueue_failed',
+			durationSaved: true
+		});
+		const form = new FormData();
+		form.set('duration', '60');
+
+		const result = await changeDurationWith(form);
+
+		expect(changeAppointmentDuration).toHaveBeenCalledExactlyOnceWith(context, {
+			appointmentId: 'appt-1',
+			durationMinutes: 60
+		});
+		expect(result).toEqual({
+			status: 500,
+			data: {
+				error:
+					'The duration was saved, but calendar and email update submission could not be confirmed.',
+				durationSaved: true
+			}
+		});
+		expect(result).not.toHaveProperty('success');
+	});
+});
diff --git a/apps/worker/src/email/builders/appointment-edited-by-host.test.ts b/apps/worker/src/email/builders/appointment-edited-by-host.test.ts
index 967bf3fa..f1b84b8e 100644
--- a/apps/worker/src/email/builders/appointment-edited-by-host.test.ts
+++ b/apps/worker/src/email/builders/appointment-edited-by-host.test.ts
@@ -1,8 +1,103 @@
 import { describe, expect, test } from 'vitest';
 import { appointmentEditedByHost } from './appointment-edited-by-host.js';
 import { sampleInput } from '../__fixtures__/appointment.js';
+import { fmtWhen } from '../format.js';
 
 describe('appointmentEditedByHost', () => {
+	test.each(['confirmed', 'pending'] as const)(
+		'duration edited from 90 to 120 minutes on a %s appointment keeps the existing recipient policy',
+		(status) => {
+			const previousAppointment = {
+				...sampleInput.appointment,
+				status,
+				end_time: '2026-01-05T16:30:00Z',
+				ics_sequence: 3,
+				note: 'Bring a laptop.',
+				video_chat: 'https://meet.example.com/room-123'
+			};
+			const input = {
+				...sampleInput,
+				appointment: {
+					...previousAppointment,
+					end_time: '2026-01-05T17:00:00Z',
+					ics_sequence: 4,
+					action_log: JSON.stringify([
+						{
+							action: 'edit',
+							actor: 'host',
+							at: '2026-01-02T10:00:00Z',
+							payload: {
+								metadata: {
+									changes: ['duration_updated'],
+									previous_duration: 90,
+									duration: 120
+								}
+							}
+						}
+					])
+				}
+			};
+
+			const messages = appointmentEditedByHost(input);
+			expect(messages.map((message) => message.role)).toEqual(
+				status === 'confirmed' ? ['guest', 'host'] : ['host']
+			);
+
+			const host = messages[messages.length - 1];
+			expect(host.to).toBe('owner@acme.test');
+			expect(host.content.subject).toBe('Updated details: 30-min with Jane Doe');
+			expect(host.content.paragraphs).toEqual([
+				'You updated the details for the appointment with Jane Doe <jane@example.com>.',
+				'You updated the duration of the appointment.'
+			]);
+			expect(host.content.rows).toContainEqual({
+				label: 'When',
+				value: fmtWhen(
+					previousAppointment.start_time,
+					'2026-01-05T17:00:00Z',
+					input.cfg.user.timezone
+				)
+			});
+			expect(host.content.rows).not.toContainEqual({
+				label: 'When',
+				value: fmtWhen(
+					previousAppointment.start_time,
+					previousAppointment.end_time,
+					input.cfg.user.timezone
+				)
+			});
+			expect(host.content.rows).toContainEqual({ label: 'Note', value: previousAppointment.note });
+			expect(host.content.rows).toContainEqual({
+				label: 'Video link',
+				value: previousAppointment.video_chat
+			});
+			expect(host.ics).toBeUndefined();
+
+			if (status === 'confirmed') {
+				const [guest] = messages;
+				expect(guest.to).toBe('jane@example.com');
+				expect(guest.content.subject).toBe('Updated details: 30-min with Acme Scheduling');
+				expect(guest.content.heading).toBe('Appointment details updated');
+				expect(guest.content.paragraphs).toEqual(['The duration of your appointment was updated.']);
+				expect(guest.content.rows).toContainEqual({
+					label: 'When',
+					value: fmtWhen(
+						previousAppointment.start_time,
+						'2026-01-05T17:00:00Z',
+						'America/Los_Angeles'
+					)
+				});
+				const ics = guest.ics?.content;
+				expect(ics).toContain('METHOD:REQUEST');
+				expect(ics).toContain('UID:appt-1');
+				expect(ics).toMatch(/^DTSTART(?:;[^:\r\n]+)?:20260105T150000Z\r?$/m);
+				expect(ics).toMatch(/^DTEND(?:;[^:\r\n]+)?:20260105T170000Z\r?$/m);
+				expect(ics).not.toContain('20260105T163000Z');
+				expect(ics).toContain('SEQUENCE:4');
+			}
+		}
+	);
+
 	test('note added on a confirmed appointment (notifies both, has guest ics)', () => {
 		const action_log = JSON.stringify([
 			{
diff --git a/apps/worker/src/email/builders/appointment-edited-by-host.ts b/apps/worker/src/email/builders/appointment-edited-by-host.ts
index 8b251995..44544646 100644
--- a/apps/worker/src/email/builders/appointment-edited-by-host.ts
+++ b/apps/worker/src/email/builders/appointment-edited-by-host.ts
@@ -53,6 +53,10 @@ export function appointmentEditedByHost(i: AppointmentEmailInput): AppointmentEm
 		paragraphs.push('The video link of your appointment was removed.');
 	}
 
+	if (changes.includes('duration_updated')) {
+		paragraphs.push('The duration of your appointment was updated.');
+	}
+
 	if (paragraphs.length === 0) {
 		paragraphs.push('The details of your appointment were updated.');
 	}
@@ -77,6 +81,9 @@ export function appointmentEditedByHost(i: AppointmentEmailInput): AppointmentEm
 	];
 
 	const hostParagraphs = [`You updated the details for the appointment with ${guestLabel(a)}.`];
+	if (changes.includes('duration_updated')) {
+		hostParagraphs.push('You updated the duration of the appointment.');
+	}
 
 	const guestEmail = {
 		subject: '',