1. "Override Maintenance Windows" unchecked in the SWU policies
2. Reboot at the end of the update cycle enabled
3. "Maintenance Window" turned on and configured
Then:
1. Updates will be installed on the clients when MW is opened (active) there
2. Reboot should be performed at the end of the update cycle
If you're observing different behavior then we'll need more information: configuration(more details)/logs/etc.
Regards,
Robert