Build a cron schedule and read it back in English — including the day-field trap.
0-59. Use * for every minute, */15 for every quarter hour.
0-23, in the clock of the machine running the job.
0 is Sunday on most systems.
At minute 0 past hour 3
Every field is unambiguous. Note that the schedule follows the clock of whatever machine holds the crontab, including its daylight-saving changes — a job set for 01:30 runs twice on one night a year and not at all on another.
0 3 * * * # At minute 0 past hour 3
What this cannot tell you
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