12 is quite a lot. I'm closer to 10 when I'm really pushing it. Work 7-7 or 8-8 with 1hr lunch/errands and 1hr exercise/day. Maybe a bit on the weekends but it's hard if you want to see friends or have any kind of social life.
Probably 55/week tops. (This is real productive work, not the 1hr of email I do when I wake up, etc.)