since Windows 8 respectively Server 2012 the policy to install Updates at a specific date and time has no affect.
Microsoft changed the behaviour for installing updates. The schedule for a installation and restart of updates is just defined by the deadline for Updates on the WSUS Server.
After installing the update the policy lets you choose to
- Installing updates due to a automatic maintenance, this is the default
- At a specific date and time, the behaviour before Windows 8 and 2012