Cron During Business Hours

0 9-17 * * 1-5

At 9 times a day on Monday, Tuesday, Wednesday, Thursday and Friday

Field by Field

Field	Value	Matches
Minute	0	0
Hour	9-17	9, 10, 11, 12, 13, 14, 15, 16, 17
Day of month	*	every day
Month	*	every month
Day of week	1-5	1, 2, 3, 4, 5

Ranges in Two Fields at Once

9-17 in the hour field and 1-5 in the day-of-week field intersect: nine runs a day (09:00 through 17:00 inclusive), Monday through Friday, 45 runs a week.

Ranges in *different* fields intersect. Restricting both day-of-month and day-of-week is the one exception, where cron takes the union instead.

Ends Are Inclusive

9-17 includes 17, so the last run is at 17:00, not 16:00. If the intent is "during the working day, finishing before people leave", 9-16 is what you want.

Every Half Hour Instead

0,30 9-17 * * 1-5 doubles the frequency inside the same window. Combining a list in the minute field with a range in the hour field is entirely legal and very common.

Holidays Are Not in Cron

There is no holiday awareness anywhere in cron. A job that must not run on public holidays needs a check in the script against a calendar you maintain — and that calendar is jurisdiction-specific, which is why most teams settle for running anyway and making the job harmless on a quiet day.

Time Zones

Standard crontab evaluates in system local time. Vercel Cron, GitHub Actions, Kubernetes CronJobs and AWS EventBridge all evaluate in UTC. If converting your local time crosses midnight, the day-of-week field shifts too — weekdays at 5pm in UTC-07:00 is 0 0 * * 2-6, not 0 0 * * 1-5.

The Day-Field Trap

When both the day-of-month and day-of-week fields are restricted, cron matches either, not both. 0 0 13 * 5 runs on every 13th *and* every Friday — not Friday the 13th. Leave one of them as * unless you genuinely want the union.

Other Common Schedules

Expression	Runs
* * * * *	Every minute
*/5 * * * *	Every 5 minutes
*/15 * * * *	Every 15 minutes
0 * * * *	Every hour, on the hour
0 0 * * *	Every day at midnight
0 9 * * *	Every day at 9am
0 9 * * 1-5	Weekdays at 9am
0 9 * * 1	Every Monday at 9am

Making the Job Safe

• Assume double firing. DST transitions, restarts and retries all cause it. Make the job

idempotent rather than assuming exactly-once.

• Assume overlap. Cron starts the next run whether or not the last one finished. Take a

lock.

• Avoid :00. Every hourly job on the internet fires at the top of the hour; a random

minute spreads load on shared APIs.

• Log the start and end. A cron job that silently stops running is invisible until

someone notices the missing output.