Cron twice a day

For standard clock-aligned cron, both match midnight and noon. The explicit 0,12 list communicates those two intended times more clearly. Expression: 0 */12 * * *

No. Use two entries, each with its own expression: 0 8 * * * and 30 17 * * *; combining both minutes and hours would create unwanted times.

Use 0 6,18 * * *. The comma-separated hour list creates two fixed wall-clock runs with the same minute. Expression: 0 6,18 * * *

Yes. 0 8,17 * * * runs at 08:00 and 17:00, creating 9-hour and 15-hour gaps rather than equal 12-hour gaps. Expression: 0 8,17 * * *

No. A list selects wall-clock times, and unequal choices produce unequal gaps; DST can also change elapsed time between local-clock runs.

Use 0 6,18 * * 1-5. The hour list selects two times and the weekday range excludes Saturday and Sunday. Expression: 0 6,18 * * 1-5

Behavior varies: Vixie/cronie can skip or double a local time; GitHub advances to the next valid time; EventBridge Scheduler skips spring's missing time and runs once during fall-back. UTC-only schedulers are unaffected.

The scheduler's timezone controls both. Configure an IANA timezone when 06:00 and 18:00 must follow a particular local clock.

Use cron(0 6,18 * * ? *). The bare editor expression includes AWS's required year field and ? in day-of-week.

Usually no. Standard cron waits for the next listed time, so add catch-up logic if both daily executions are required.

Yes. Crontap can run 0 0,12 * * * in the selected IANA timezone and invoke an HTTP endpoint at both times.

0 0,12 * * *. Paste this into Linux crontab, Vercel cron, node-cron, robfig/cron, or a Kubernetes CronJob to run a job twice a day (midnight and noon); AWS EventBridge and Quartz need the six-field form.

The editor above shows the next 30+ runs on a calendar in your local timezone, plus a plain-English description. If the calendar matches your intent, the cron is correct.

Linux crontab, Vercel cron jobs, node-cron, robfig/cron, and Kubernetes CronJob accept the five-field form as is. AWS EventBridge and Quartz use six-field expressions with a ? in one of the day fields; see the AWS and Quartz guides for the conversion. Vercel's free Hobby plan caps the minimum frequency at once-per-day; the Pro plan removes that cap.

Most schedulers will start the new run anyway, leading to overlap. To prevent this, wrap the command with flock -n /tmp/myjob.lock /path/to/script.sh on Linux, or set concurrencyPolicy: Forbid on Kubernetes CronJob. Vercel and EventBridge may overlap runs if the previous one is still executing; make the handler idempotent.