Thanks everyone. Several good ideas here. When you actually start thinking about it, overnight updates like that really do seem wasteful. They're probably updating for what, an hour on one day per week? And then the computer just sits idling until 8am... yeah, it's time for a change. My previous district was in the US and had over 6k devices- energy use wasn't a concern as long as the devices were ready to use at a moment's notice. The UK is more conscious about matters like this, so I'm having to approach things differently.
I think I will play with the schedule and try to get it to do updates much earlier and then do a full shutdown nightly.
Cheers!