Not less than 1hour of slowly rising tension til both of you explode with streams of ecstasy shooting from your cocks. Preferably 2 or 3 hour sessions
Definitely longer is better! It takes time to work up to a nice hot sweaty dick grind. The utimate goal is the connection two dudes make which again takes some time. Nothing like that squishy sound two hard dicks make after shooting that hot nutt all over each others pubes. Damn...why would anyone want to rush that? Hard now just thinking about it.