Sorry but this is the same time eBay does theirs. I agree the slowest is Friday night into Saturday morning but we don't have anyone working then. Thursday night into Friday morning is the 2nd slowest which is why we, and I assume eBay does it then too.
If something goes wrong we need to have people around and that is better Thursday nights than Friday.
We monitor tens of millions of auctions a week and this is the slowest time next to Friday night. That's based on all auctions. Your category and items may vary but we're going with the averages here. If we switched it to another time then another group of users bigger than yours would complain that that time was horrible.
We're working on a database update which should be completed in the next 3 months which will allow us to minimize the maintenance window. Hopefully to under 2 hours and possibly maybe even 1 hour, or we may be able to go every other week or something like that.