Hi Romaric. Autopatch uses a combination of active hours along with update compliance deadlines to schedule device reboots. If Windows can't find a time to update outside of active hours, users will be notified, and a reboot will need to be scheduled within active hours.  In answer to your question: a user can reschedule/postpone if necessary, but isn't able to reschedule past the deadline.

This Autopatch Doc outlines the typical End user experience and some scenarios which you might find useful: End user experience - Windows Deployment | Microsoft Docs