Nobody has mentioned this factor so I will be the first one to do it. Some may say its not important, I think its pretty important.
I have alternated between long 2/3hr punts to 30min punts in my punting lifetime. And I can say I have been punting for 10 years now and I can remember pretty much every single detail of those long punts. As in what happened, what the girl looked like, what we did, what we said and all sorts.
The 30min punts I cannot remember them at all. Sometimes I have even forgotten I had them until I look at my past reviews.
So if people are like me, do you pay just for the experience in the here and now and nothing more than this, or having the long term memory of that experience too. I think having the long term memory of it is better and not just totally forgetting you did anything a couple of years later.
Even though I don't have your photographic memory I, broadly speaking, agree with you on this, Anth.
So I think longer is best. And overnighters even better. As you will remember them for a long time afterwards
However, this is where our opinions might diverge. In my experience, you might need to clarify the t's & c's of an Overnight before you confirm the booking.
I'd had a number of enjoyable Overnights with a number of SPs before I met my last, now-retired, Regular. She didn't have Overnights on her tariff so, having had two or three 1-hour appointments with her, I enquired about the possibility of such a meeting.
I paraphrase her reply which went on the lines of, "Well if you want to lie next to me in the small hours of the morning, listening to me sleeping, you can. But wouldn't you prefer the better value of a 4-hour daytime appointment when we can do anything that's on my AW 'Likes List'?"
As one whose friends think he was born frugal

, I saw the logic of what she was saying! So that's what we did once a month until she left 'the industry'. But, as I say, I couldn't claim to recall all those meetings.