Too much time...not enough time.

Is there an optimum length of time a session should last.

IMHO, NO, every individual is different in their psychological makeup, approach and desired goals. The optimal length of time for your Anerosession is totally determined by YOU. Check out the user Polls How long is just right to ride your Aneros? & How frequently do you use your massager? to see the range reported by your fellow Anerosians.

Is it possible that I could hinder my sensitivity or
csuse some underlying problem or even damage?

I doubt you would do any damage if you are using the device hands free and as per the manufacturers instructions. However, I think too frequent usage may cause a temporary loss of sensitivity as the nerves may get overstimulated and start to deplete their neurotransmitter chemicals which then impairs signal transmission to the brain. Your mind determines what is pleasurable based upon the sensory signals returned from the body and interpreted in the brain. When those chemical messengers are impaired the whole sensory interpretation gets distorted and diluted. Rest time allows the body to replenish those chemicals and restore them to normal functioning.

Some of the “ Orgasms” I have are very intense indeed and can last for five or ten minutes. I am breathless when they cease but I’m sure they’re not a super Os but I feel not far off it.

Why are you sure they are NOT Super-O's? It sure sounds like they fit the definition for a Super-O to me, I certainly hope you are not discounting yourself based upon some misconstrued idea of what a Super-O is. You may find reading the threads Super-O Myths & Illusions, @neros thread The Myth of Super Orgasm & @Buster 's thread What exactly is a Super-O? to get a wider perspective of what a Super-O is in reality.
Good Vibes to You !

Thank you Rumel. You’re correct. How do I know that my orgasms are not super Os? I don’t. But I’m beginning to think that the super O is at the pinnicle of one’s own experience. One can go shorter or longer but not upwards. My experience it that point where is no more height or extension to go. That’s it. Ones own pinnacle . No need to extend . One has reached the limit of ones capability. I wonder if that makes sense? I believe I’ve had Super Os and been unaware of it!!

I’m beginning to think that the super O is at the pinnicle of one’s own experience. One can go shorter or longer but not upwards. My experience it that point where is no more height or extension to go. That’s it. Ones own pinnacle . No need to extend . One has reached the limit of ones capability. I wonder if that makes sense?

A I've frequently noted, the Aneros journey is an evolving adventure with no end point to the journey and each man's adventure is unique to his circumstances. Any limit that you propose is really just a self imposed one, as your consciousness expands the envelope of perceived limits expands with it. Your pinnacle today may be expanded tomorrow just by your own thought processes and the richness of your Super-O's can deepen as you comprehend more and more subtleties of sensation. This expansion of limits is not just up/down, it is omnidimensional, including the dimension of time. Today's experience is a fractal of tomorrow's, how it scales is determined by your mind set. You are more powerful and creative than you know, why think you have already reached your peak?
Good Vibes to You !

On occasion for whatever reason I have cut a session to less then an hour,and had another a few hours later.The pleasure level goes from 0 to 70 mph in 15 sec.Aneros use is not an exact science. When I cut a session short the urge to have another sometimes can be overwhelming,but I have also experienced the opposite.Sometimes I wonder if the moon makes a difference.As for super o or not a super o it's kinda like driving through Estes Park you should enjoy what is right in front of you rather then thinking about what is 10 miles ahead.

Looking for the Super O is probably distracting. It takes you from the here and now to a imagined future.
forget the SO and enjoy the moment .