[TippetsTX]

I believe advancement pacing is a factor as well. This is also extremely variable, though. Players want to see their characters progressing so if my game sessions are infrequent (say monthly) I might be willing to grant a bit more XP than I would if we were playing weekly.

But this really depends on the group. If you're just starting out (and playing infrequent, but unusually long sessions) choose a baseline you are comfortable with and then increase by 10, 20 or 30% for above-and-beyond actions. This could be something like 10 or 20 XP per hour played (plus bonuses, if applicable). This will allow your players to experience several bumps in ability over the course of a long weekend.