I have mine booked for 4 hours. I know that a lot of my guests are really going to enjoy to unlimited beer and wine and the dance floor : ) Most of my friends are the kind that have been know to stay up socialing till the sun comes up. If it was
allowed I think they'd prefer if the party went to 2 in the morning.
I think it really depends on the time of day. Some of my friends have had just a luncheon reception. Those don't last as long. We are having an appetizer and dessert reception starting at 8. It is still going to go until midnight though. If you
are having a full meal, that will certainly increase the amount of time spent at the reception. There is no rule, however, about you not leaving early. Once you have finished whatever traditions you are going to cover why not sneak out? That is what
my FI and I are going to have to do. My family has a long tradition of messing with the newlyweds and we have had to be super secretive as to where we are going and when we are returning lol