Cron Expression for Every Minute: * * * * *

Field by field

* * * * * reads: Every minute. That is 1,440 runs a day.

1,440 runs a day. If one run can take longer than a minute, runs overlap: guard the job with a lock (flock -n) or it will pile up.
GitHub Actions will not run a schedule more often than every 5 minutes, so this becomes every 5 minutes there at best.
Cron cannot go below a minute. For every 30 seconds, run two entries - one plain, one that starts with sleep 30; - or use a timer.

* 9-17 * * 1-5Every minute, but only during office hours on weekdaysExplain it
*/2 * * * *Every other minuteExplain it

* * * * * /path/to/job.sh

Runs in the machine's local timezone. crontab -e to edit.

on:
  schedule:
    - cron: "* * * * *"

Always UTC. Nothing more often than every 5 minutes, and runs can start late when GitHub is busy.

spec:
  schedule: "* * * * *"
  timeZone: "Asia/Kolkata"

timeZone needs Kubernetes 1.27 or later; without it the controller's zone applies, usually UTC.

@Scheduled(cron = "0 * * * * *")

Six fields: seconds come first. Days are written as names, which Spring and cron read alike.

0 * * * * ?

One of day-of-month and day-of-week must be ?. Quartz counts days 1-7 from Sunday, so names are safer than numbers.

cron(* * * * ? *)

Six fields, the last one the year. UTC unless the schedule sets a timezone. Days count from Sunday, as in Quartz.

[Timer]
OnCalendar=*-*-* *:*:00
Persistent=true

Persistent=true runs a job that was missed while the machine was off, once it is back.