fix: adjust the plex watchlist sync schedule to have fuzziness (#3502)

also fixes the schedule making it uneditable

Author: sct

server/job/schedule.ts

@@ -8,6 +8,7 @@ import type { JobId } from '@server/lib/settings';
 import { getSettings } from '@server/lib/settings';
 import watchlistSync from '@server/lib/watchlistsync';
 import logger from '@server/logger';
+import random from 'lodash/random';
 import schedule from 'node-schedule';
 
 interface ScheduledJob {
@@ -60,21 +61,31 @@ export const startJobs = (): void => {
     cancelFn: () => plexFullScanner.cancel(),
   });
 
-  // Run watchlist sync every 5 minutes
-  scheduledJobs.push({
+  // Watchlist Sync
+  const watchlistSyncJob: ScheduledJob = {
     id: 'plex-watchlist-sync',
     name: 'Plex Watchlist Sync',
     type: 'process',
-    interval: 'minutes',
+    interval: 'fixed',
     cronSchedule: jobs['plex-watchlist-sync'].schedule,
-    job: schedule.scheduleJob(jobs['plex-watchlist-sync'].schedule, () => {
+    job: schedule.scheduleJob(new Date(Date.now() + 1000 * 60 * 20), () => {
       logger.info('Starting scheduled job: Plex Watchlist Sync', {
         label: 'Jobs',
       });
       watchlistSync.syncWatchlist();
     }),
+  };
+
+  // To help alleviate load on Plex's servers, we will add some fuzziness to the next schedule
+  // after each run
+  watchlistSyncJob.job.on('run', () => {
+    watchlistSyncJob.job.schedule(
+      new Date(Math.floor(Date.now() + 1000 * 60 * random(14, 24, true)))
+    );
   });
 
+  scheduledJobs.push(watchlistSyncJob);
+
   // Run full radarr scan every 24 hours
   scheduledJobs.push({
     id: 'radarr-scan',