To followup on this post: http://sms-hints-tricks.blogspot.com/2015/05/override-sccm-reboot-time.html
Say you just wanted simply extend the reboot of machine by a few hours and not permanently?
Simply edit the registry:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SMS\Mobile Client\Reboot Management\RebootData\ InitiatedTimeStamp
Add the number of seconds you wish to have then kill the ScNotification.exe process and restart the SMS Agent Host.
When this happens the SCNotification application should kick back in after a few seconds. It will read the changed registry value and use the new time for the reboot.
