Usually around an hour and a half to two hours. It usually takes my P gland a good half hour to really get buzzing. After that, I don't want to miss any surprises, so I will go as long as I can, when either the clock or my bladder tells me it is time for bed.
I chose the 1-2 hours. Usually 30 minutes to relax. Then breath and move the aneros for 30 minutes. If I don't feel anything I take it out and add to my cum retention.
On average it has taken me 2-3 hours to get to the point where I'm feeling much. Sometimes I get bored and fall asleep after an hour and end up waking up halfway through the night to try again. I will say that this is only possible with the Helix Syn and a lot of ID Glide. I have the Helix Syn Trident as well but that seems to be a different kind of silicone that is more velvety but dries out quicker.
I recently had my first dry O (and then another! and another!)) after 40 min or so - I can't think of anything else now! To think that some of you guys are going for 2 to 3 hours blows my mind. My wife is not a fan so I have to wait till she leaves the house but, oh my goodness, I can't wait till she leaves so I can try going for as long as some of you! I am in my 50's but I feel like a kid again!