@Mountain Pond, thanks for posting in the Q&A.
Based on my understanding, when the device has installed the update, it will come to restart pending, before the device has reached the grace period, it will pop up that the device will reboot after the grace period, and when it finally reaches the end of the grace period, it will pop up that the device will reboot in a few minutes.
For rebooting during non-working hours, you can configure automatically install and reboot during maintenance hours and device active time range so that when the device is active during working hours, the device will not reboot, it will automatically reboot during non-active hours.
Meanwhile, for the setting "Auto reboot before deadline", if it is set Yes, then the device has installed updates and is outside of active hours, it might attempt an automatic restart before the deadline. If it is set No, devices will delay automatically restarting until both the deadline and grace period have expired, even if applicable updates are already installed and pending a restart.
https://learn.microsoft.com/en-us/mem/intune/protect/windows-update-settings
Hope it will help.
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