I voted none, as I don't really prepare for school the day before. After breakfast, the kids play for a little while, and that's when I get our stuff together. Probably less than 15 minutes on average though. I just pull out our reading, skim over the math and get out any manipulatives, etc., and then just improvise anything/everything else. I've tried the workbox thing - filling those spaces the night before - and I found that I just feel less stressed about the whole thing if I go into the morning without any great expectations about what will get accomplished that day. So no more workboxes, and yeah, I'm liking just winging it for now.