I'd like to wear one for hours and wonder what your experience was like.
The most immediate time-limit is lube, you'll want something that doesn't dry out. Water-based lubes have a limited time-span of usefulness. Generally speaking though, I think aneros sessions benefit more from quality over quantity. You can wear it for hours and hours, but if your brain is tuning it out the whole time, I see questionable benefit.
IMO a tuned-out prostate massage, is just going to be a tuned-out sensation no matter how long you do it. There is no brute-force approach. Not clenching harder, not wearing longer. You have a finite window of physical sensitization, in which to also get your mind into the game. And both are required.
At least that's my opinion. But I've never heard of a super-o success story where the guy was wearing it for hours and hours, and somewhere out of the blue a super orgasm hit.
The mind is very good at tuning-out sensory data that is constant but unimportant. Try listening to white-noise for an hour, and see if you forget you're listening to it. I consider prostate pressure to be similar.
I've never had any success with Aneros when there's been external stimulation that I couldn't tune out. For example, I can never progress if I'm listening to a podcast or similar, but ambient noise coming in through an open window has never been a problem.