Maybe it's me, but I have no problem staying late on a Friday to fix my screw-up. However, I'm terrified of having to fix something Monday morning while everyone else is watching.

But the real reason we deploy weekday mornings is so everyone is on deck and we can get outside help if required. When I was doing system integration, the problem was never in my code, it was the vendor's. Testing can only get you so close to the real world.