Software updates need a 'hard' deadline so that computers who have hit the updates but never leave their computers on within a maintenance windows, will never have the updates installed.

1st : Deployments made available for users to install at their leisure from the software center. Possible

2nd : After say 1 week, install the updates as per maintenance windows in the evening. Possible

3rd : After 1 more week if not yet installed, just install no matter what at any time, with the standard notifications for reboots as per SCCM client settings. "Currently not possible"

https://social.technet.microsoft.com/Forums/en-US/6f8f161c-45e2-4a1a-b78c-dd1f7c0bbc0c/software-updates-adrs?forum=ConfigMgrCompliance