FATE (FAE) stunts /session
Consider how much your group accomplishes in a typical tabletop session. Usually, there's some sort of sense of having reached a suitable plot-point on which to pause the game.
I take this idea and say that at "suitable plot points" we'll call it a "session" and offer the Refresh and stunt-refresh. Depending on the pace of the game, that might still be months before it happens.
I just wrapped up the first scene in a Dresden Files game. Combat is over... it's a suitable point at which to call it the end of the session. Either way, there should be some sort of sense of accomplishment (good or bad).