Still incredibly odd and narrow of a time slot. I wonder if any major releases would cause server strain.
You raise an interesting point about the narrow time slot. Now that I think about it, isn't this restriction simply going to dissuade indie or small developers from releasing mature content? It's probably difficult enough for developers to release mature games on a Nintendo console; forcing potential buyers to fit their purchasing habits into an inconvenient 4 hour time frame certainly isn't going to do sales any favours.
As you say, it's an incredibly odd decision on NoE's part.
I don't see how this decision can be justfied in terms of adhering to European legislation. I'm pretty sure Microsoft, Sony, Valve and others don't have any such restrictions. It's bizarre.