2 hours is my go to. 3 hours on occasion. I dont have enough activities to fill much longer. Like some have mentioned i also enjoy chatting before and after to build a little of a relationship. If its 3 hours i normally build breaks in for both of us.

When i do longer than that is normally a mix of social time and session time which i also like. For what its worth if we are doing a session and a dinner i like doing dinner after the session. I think that is opposite of most people but hey im weird i guess :-).