A cron expression is a string that defines a schedule for executing a task. If you want a schedule that spans multiple hours but starts at an arbitrary minute, you can achieve this by carefully configuring the fields of the cron expression.

Syntax Recap:

Cron expressions follow this format:

<day_of_month> <day_of_week>

minute: 0-59

hour: 0-23

day_of_month: 1-31

month: 1-12

day_of_week: 0-7 (where both 0 and 7 represent Sunday)

Problem: Arbitrary Start Minute Across Multiple Hours

To run a task every hour, starting at an arbitrary minute (e.g., 15 minutes past the hour) across multiple hours (e.g., between 10 AM and 4 PM), the solution involves specifying both the minute and hour ranges.

Example 1: Run Every Hour at :15 Between 10 AM and 4 PM

The cron expression:

15 10-16 * * *

minute: 15 — starts at 15 minutes past the hour.

hour: 10-16 — spans from 10 AM to 4 PM.

Other fields (*) are set to their defaults, meaning the job runs every day, every month, and every day of the week.

Example 2: Run Every Hour at :45 Between 8 AM and 6 PM

The cron expression:

45 8-18 * * *

minute: 45 — starts at 45 minutes past the hour.

hour: 8-18 — spans from 8 AM to 6 PM.

Other fields are unchanged.

Additional Notes

1. Multiple Arbitrary Minutes: If you want multiple specific minutes (e.g., 15 and 45 past the hour):

15,45 10-16 * * *

2. Every X Minutes: If you want the task to repeat every 30 minutes across multiple hours (e.g., starting at :10 and continuing every 30 minutes):

10/30 10-16 * * *

3. Advanced Scheduling: Use tools like crontab.guru to validate your cron expressions.