As someone who plays with Hackenslash 3-4 hours is about the average time we manage. Sometimes we play less and talk more and sometimes we get wasted time as well.
It would be nice to play longer sessions or to occasionally have a much longer session but the question is when we could fit it in. Two of us have children and we all have work the next morning so playing to 2 or 3 in the morning isn't possible anymore like we did years ago where we used to have 7-8 hour sessions.
Hackenslash - maybe we should aim to start by 7pm or something and get an extra hour in, or maybe once a month, couldn't imagine any more frequently with other commitments, we could play for a longer period but it couldn't be at Gary's as we have a limit of midnight there.
On DM prep time I agree, it would be nice to see how long others spend in prep and what they prep.