I absolutely prefer long and drawn out "sessions" that last for days or even weeks. However, I have special sort of hybrid Pro/Lifestyle relationships with certain Pro Dommes that have a lot more service involvement than dungeon-style play. They all started as normal hourly play, but have somehow morphed into situations that extend way beyond what I could afford if it was a normal Pro/client per-hour session.

But, to better answer what you are asking... What I book for sessions is generally 90 minutes to 2 hours because that hits the limits I put on myself for the amount I will pay for a given visit/session. But, at the end, I still always want more and it is just my self-discipline that stops it from going on.