Three Fridays a month, from 8-12, or thereabouts. I have an hour drive to the game, so I usually have to call it quits around 12, but sometimes everybody else stays some time longer.
Fridays work reasonably well, though my girlfriend doesn't like it too much. She would never go so far as to ask me not to game on Fridays, but she has made a point that on any Friday when I don't game, I should let her know. She doesn't dislike me gaming on Fridays, or not like me gaming, we just are always busy during the week, so we try to find time on weekends.
It's nice to spend a nice relaxing Friday night gaming, and then play rugby Saturday. A night of sitting around followed by a day of running around.