As far as time? At least 2 hours. It allows enough time to drop into the scene and it not feel rushed. Unless someone wants something simple. An hour is good for Foot Dom or spanking but not much else.

Sometimes I get a sub who underestimates how much time it takes to do everything on their list. It usually less experienced players. I just help them trim things down. I mean, I could do the equivalent of a shopping spree where you're running around grabbing as much off the shelf as you can before the time runs out...but that's not sexy.