Sometimes TimerTrigger function triggers a bit earlier

Question

I have the TimerTrigger function with the CRON 0 * * * * *, according to documentation this function should be triggered every minutes at 00 seconds, for example 7:06:00.
But occasionally it is fired a bit earlier, for example 07:05:59.

Does anyone know why this happens?

Answer 1

Similar question here: https://learn.microsoft.com/en-us/answers/questions/46724/how-accurate-is-the-time-in-azure-functions.html

Timer Functions aren't guaranteed to be perfect in their timing- in this particular case there appears to be a few milliseconds of drift between firing and logging. Likely if you were to check the other invocations details would show they were first a few milliseconds after the minute. You can mitigate this some by using a dedicated VM so you can control how the timer is fired, but it is unlikely that you will eliminate this completely.