I am not sure if you want your SEPM or all your "Servers with SEP Client installed" to update at night-Time only.
You could realize this with the use of eithe a Live-Update Administrator (LUA) server that is scheduled to only load Updates at night. (this won't stop the heartbeat-function of the Server-Clients, but they will not be notified of a new update until the LUA actually downloaded one.
Or you could also use a dedicated GUP for those Clients which you simply shut down during daytime and reboot in the evening.
Anyway you choose: From a security-point of view you will significantly weaken your defense when you are not deploying def-updates as fast as possible.
Best regards
Stephan