Your best option is to tell it to restart, but rather set this to be a rolling deadline.
Create a rolling deadline to ensure that the computers DO end up restarting, but not when your clients don't want them to.
Setting it to my suggested guidance of 5 days with a 2 day grace period, will allow a computer to schedule the restart ONLY IF THE USER IS NOT LOGGED IN, as soon as it can within the 5 days. My guide also shows you how to add the notifications that the user will see to let them know they need to restart within a time. They can schedule the restart when it's convenient for them (assuming within the 5 day deadline).
If the user logs out anytime within that 5 day period, and the computer is idle, Windows will restart and apply the update which preserves compliance and doesn't affect the user - a win-win.
What specifically is the reason why you're trying to prevent it from restarting?