diff --git a/app/client/modules/backups/components/schedule-mirrors-config.tsx b/app/client/modules/backups/components/schedule-mirrors-config.tsx
index 759d6754..f4c82653 100644
--- a/app/client/modules/backups/components/schedule-mirrors-config.tsx
+++ b/app/client/modules/backups/components/schedule-mirrors-config.tsx
@@ -1,4 +1,4 @@
-import { useMutation, useQuery, useQueryClient, useSuspenseQuery } from "@tanstack/react-query";
+import { useMutation, useQuery, useSuspenseQuery } from "@tanstack/react-query";
 import { Copy, Plus, RefreshCw, Trash2 } from "lucide-react";
 import { useEffect, useMemo, useState } from "react";
 import { toast } from "sonner";
@@ -22,7 +22,6 @@ import {
 	getScheduleMirrorsOptions,
 	getMirrorCompatibilityOptions,
 	getMirrorSyncStatusOptions,
-	getMirrorSyncStatusQueryKey,
 	updateScheduleMirrorsMutation,
 	syncMirrorMutation,
 } from "~/client/api-client/@tanstack/react-query.gen";
@@ -32,10 +31,10 @@ import { RepositoryIcon } from "~/client/components/repository-icon";
 import { StatusDot } from "~/client/components/status-dot";
 import { ByteSize } from "~/client/components/bytes-size";
 import { useServerEvents } from "~/client/hooks/use-server-events";
-import { format, formatDistanceToNow } from "date-fns";
 import { cn } from "~/client/lib/utils";
 import type { GetScheduleMirrorsResponse } from "~/client/api-client";
 import { Link } from "@tanstack/react-router";
+import { useTimeFormat } from "~/client/lib/datetime";
 
 type Props = {
 	scheduleShortId: string;
@@ -69,14 +68,29 @@ const buildAssignments = (mirrors: GetScheduleMirrorsResponse) =>
 	);
 
 export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, repositories, initialData }: Props) => {
-	const queryClient = useQueryClient();
+	const { formatDateTime, formatTimeAgo } = useTimeFormat();
 	const [assignments, setAssignments] = useState<Map<string, MirrorAssignment>>(() => buildAssignments(initialData));
 	const [hasChanges, setHasChanges] = useState(false);
 	const [isAddingNew, setIsAddingNew] = useState(false);
 	const [syncDialogMirrorId, setSyncDialogMirrorId] = useState<string | null>(null);
 	const [selectedSnapshotIds, setSelectedSnapshotIds] = useState<Set<string>>(new Set());
+	const [syncDialogOpen, setSyncDialogOpen] = useState(false);
 	const { addEventListener } = useServerEvents();
 
+	const closeSyncDialog = () => {
+		setSyncDialogOpen(false);
+		setTimeout(() => {
+			setSyncDialogMirrorId(null);
+			setSelectedSnapshotIds(new Set());
+		}, 300);
+	};
+
+	const openSyncDialog = (mirrorShortId: string) => {
+		setSyncDialogOpen(true);
+		setSelectedSnapshotIds(new Set());
+		setSyncDialogMirrorId(mirrorShortId);
+	};
+
 	const { data: currentMirrors } = useSuspenseQuery({
 		...getScheduleMirrorsOptions({ path: { shortId: scheduleShortId } }),
 	});
@@ -106,17 +120,11 @@ export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, re
 
 	const { data: syncStatus, isLoading: isSyncStatusLoading } = useQuery({
 		...getMirrorSyncStatusOptions({
-			path: { shortId: scheduleShortId, mirrorShortId: syncDialogMirrorId! },
+			path: { shortId: scheduleShortId, mirrorShortId: syncDialogMirrorId ?? "" },
 		}),
 		enabled: syncDialogMirrorId !== null,
 	});
 
-	useEffect(() => {
-		if (syncStatus?.missingSnapshots) {
-			setSelectedSnapshotIds(new Set(syncStatus.missingSnapshots.map((s) => s.short_id)));
-		}
-	}, [syncStatus]);
-
 	const toggleSnapshotSelection = (shortId: string) => {
 		setSelectedSnapshotIds((prev) => {
 			const next = new Set(prev);
@@ -142,7 +150,7 @@ export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, re
 		...syncMirrorMutation(),
 		onSuccess: () => {
 			toast.success("Full sync started");
-			setSyncDialogMirrorId(null);
+			closeSyncDialog();
 		},
 		onError: (error) => {
 			toast.error("Failed to start sync", {
@@ -195,11 +203,6 @@ export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, re
 					});
 					return next;
 				});
-				queryClient.removeQueries({
-					queryKey: getMirrorSyncStatusQueryKey({
-						path: { shortId: scheduleShortId, mirrorShortId: event.repositoryId },
-					}),
-				});
 			},
 			{ signal: abortController.signal },
 		);
@@ -289,7 +292,7 @@ export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, re
 			return "Syncing...";
 		}
 		if (assignment.lastCopyAt) {
-			return formatDistanceToNow(new Date(assignment.lastCopyAt), { addSuffix: true });
+			return formatTimeAgo(assignment.lastCopyAt);
 		}
 		return "Never";
 	};
@@ -307,6 +310,8 @@ export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, re
 		return "Never copied";
 	};
 
+	const selectedMirrorRepo = repositories.find((r) => r.shortId === syncDialogMirrorId);
+
 	return (
 		<Card>
 			<CardHeader>
@@ -443,14 +448,14 @@ export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, re
 															<Button
 																variant="ghost"
 																size="icon"
-																onClick={() => setSyncDialogMirrorId(repository.shortId)}
+																onClick={() => openSyncDialog(repository.shortId)}
 																disabled={isSyncing(assignment) || hasChanges}
 																className="h-8 w-8 text-muted-foreground hover:text-foreground"
 															>
 																<RefreshCw className={cn("h-4 w-4", isSyncing(assignment) && "animate-spin")} />
 															</Button>
 														</TooltipTrigger>
-														<TooltipContent>Sync all snapshots</TooltipContent>
+														<TooltipContent>Sync more snapshots</TooltipContent>
 													</Tooltip>
 													<Button
 														variant="ghost"
@@ -481,22 +486,16 @@ export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, re
 					</div>
 				)}
 
-				<Dialog open={syncDialogMirrorId !== null} onOpenChange={(open) => !open && setSyncDialogMirrorId(null)}>
+				<Dialog open={syncDialogOpen} onOpenChange={(open) => !open && closeSyncDialog()}>
 					<DialogContent>
 						<DialogHeader>
 							<DialogTitle>Sync snapshots</DialogTitle>
 							<DialogDescription>
-								{syncDialogMirrorId &&
-									(() => {
-										const mirrorRepo = repositories.find((r) => r.shortId === syncDialogMirrorId);
-										return mirrorRepo
-											? `Sync all missing snapshots to "${mirrorRepo.name}"`
-											: "Sync all missing snapshots to mirror";
-									})()}
+								{`Sync missing snapshots to ${selectedMirrorRepo?.name || "mirror repository"}.`}
 							</DialogDescription>
 						</DialogHeader>
 
-						{isSyncStatusLoading ? (
+						{isSyncStatusLoading && !syncStatus ? (
 							<div className="py-6 text-center text-muted-foreground text-sm">Loading snapshot status...</div>
 						) : syncStatus && syncStatus.missingSnapshots.length === 0 ? (
 							<div className="py-6 text-center text-muted-foreground text-sm">
@@ -536,9 +535,7 @@ export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, re
 														/>
 													</TableCell>
 													<TableCell className="font-mono text-xs">{snapshot.short_id}</TableCell>
-													<TableCell className="text-sm">
-														{format(new Date(snapshot.time), "yyyy-MM-dd HH:mm")}
-													</TableCell>
+													<TableCell className="text-sm">{formatDateTime(new Date(snapshot.time))}</TableCell>
 													<TableCell className="text-right text-sm">
 														<ByteSize bytes={snapshot.size} base={1024} />
 													</TableCell>
@@ -551,7 +548,7 @@ export const ScheduleMirrorsConfig = ({ scheduleShortId, primaryRepositoryId, re
 						) : null}
 
 						<DialogFooter>
-							<Button variant="outline" onClick={() => setSyncDialogMirrorId(null)}>
+							<Button variant="outline" onClick={closeSyncDialog}>
 								Cancel
 							</Button>
 							<Button
diff --git a/app/server/modules/backups/__tests__/backups.mirror-sync.test.ts b/app/server/modules/backups/__tests__/backups.mirror-sync.test.ts
index e7f07b87..c81cf4fd 100644
--- a/app/server/modules/backups/__tests__/backups.mirror-sync.test.ts
+++ b/app/server/modules/backups/__tests__/backups.mirror-sync.test.ts
@@ -1,4 +1,5 @@
 import { afterEach, describe, expect, test, vi } from "vitest";
+import waitForExpect from "wait-for-expect";
 import { backupsService } from "../backups.service";
 import { createTestVolume } from "~/test/helpers/volume";
 import { createTestBackupSchedule } from "~/test/helpers/backup";
@@ -148,8 +149,7 @@ describe("getMirrorSyncStatus", () => {
 
 describe("syncMirror", () => {
 	test("should trigger sync and return success", async () => {
-		const { mockCopy } = setup();
-		const copyMock = mockCopy();
+		setup();
 		const volume = await createTestVolume();
 		const repository = await createTestRepository();
 		const mirrorRepository = await createTestRepository();
@@ -185,6 +185,52 @@ describe("syncMirror", () => {
 		).rejects.toThrow("Mirror is already syncing");
 	});
 
+	test("should reject concurrent sync requests once a sync has started", async () => {
+		const { mockCopy } = setup();
+		const copyMock = mockCopy();
+		let releaseCopy: (() => void) | undefined;
+		const copyStarted = new Promise<void>((resolve) => {
+			copyMock.mockImplementation(
+				() =>
+					new Promise((copyResolve) => {
+						releaseCopy = () => copyResolve({ success: true, output: "" });
+						resolve();
+					}),
+			);
+		});
+
+		const volume = await createTestVolume();
+		const repository = await createTestRepository();
+		const mirrorRepository = await createTestRepository();
+		const schedule = await createTestBackupSchedule({
+			volumeId: volume.id,
+			repositoryId: repository.id,
+		});
+		await createTestBackupScheduleMirror(schedule.id, mirrorRepository.id);
+
+		await expect(
+			backupsService.syncMirror(schedule.shortId, mirrorRepository.shortId as ShortId, ["snap1"]),
+		).resolves.toEqual({ success: true });
+
+		await copyStarted;
+
+		await waitForExpect(async () => {
+			const mirrors = await backupsService.getMirrors(schedule.shortId);
+			expect(mirrors[0]?.lastCopyStatus).toBe("in_progress");
+		});
+
+		await expect(
+			backupsService.syncMirror(schedule.shortId, mirrorRepository.shortId as ShortId, ["snap1"]),
+		).rejects.toThrow("Mirror is already syncing");
+
+		releaseCopy?.();
+
+		await waitForExpect(async () => {
+			const mirrors = await backupsService.getMirrors(schedule.shortId);
+			expect(mirrors[0]?.lastCopyStatus).toBe("success");
+		});
+	});
+
 	test("should throw if mirror is not configured for the schedule", async () => {
 		setup();
 		const volume = await createTestVolume();