Well it really depends on what kind of sex you are having, who with, when and how often you have had sex recently. A few years ago after my wife thought we weren't having as much sex as we used to I started a dairy of sex between us and also with others in the swing scene and it's quite surprising as quite often it seems we don't have a lot of sex yet we still average roughly once every 2.2 days!!!! Yep I worked out the percentage.
But some of those 'sessions' may only last 5-10 minutes because either we are both tired and it's the closeness we went or we have had sex several times in the last few days or just feel like a quick one lol. Other times we dress up, well she does, in something sexy and actually play can last 1-2 hours (or more at a club) often me going down on her for 30-45 minutes, some fucking, some other intimate play etc etc etc and even then after we have finished there may be lots of touching and caressing.
Now when we go only holiday things kick up a serious notch or two, so when we go to Cap D'Agde or La Mirage in Gran Canaria, we have sex between each other at least once every day/night and it's usually more than an hour every time. Then you add on the play with others often 2-4 times in a week means at the end of the holiday we are knackered (exhausted).
But when we play for the longest is when we play with other couples, Tina can go for a long time, 2-3 hours without stopping and has done in the past with several guys (and women) and when we meet a couple we hope to play (including foreplay, the sex and the after play) for a couple of hours at the very least. Regrettably many couples don't want this and just want a quick fuck so it has been hard to find couples that are attractive and want to enjoy the full experience as we do.
When we do meet the right couple we can play for several hours, of course taking a break or two but most of that time is being intimate with each other. We also have played and slept with other couples overnight, in the morning you can barely walk!!! But that is rare.
So to answer your question we have good/great sex (the actual intercourse part) that often lasts 5-10 minutes but quite often lasts 2-3 hours (at least). It just depends on the moment.
Hope that was of interest.