Back before the internet came about, I did it once or twice. In the day there was only phone book agency girls, and they weren't known for MSOG, GFE, or wanting to stay any longer than it took you to pop. Like you say, what's the point of paying for an hour when you're only likely to use 15 minutes?
There was one who was fine as hell, as fine as a phonebook girl can get. Ass for days, supernice tits, the whole nine. I used to dick her down like I was the king of porn or something. She was so good, the first time I saw her I bussed in 5 minutes. Not only that, but she had my dick sore for 4 days (the feel good kind of sore). Whenever I planned to see her again, I would rub one out about an hour beforehand. If she was MSOG, I would've just held out and tore it up for the whole hour.
Those were back in my younger days, when I could go all damn day.
Nowadays, I'm merely reduced to one shot wonder status, and there's no need to rub one out beforehand. If the desire to stretch out time is wanted today, I'd simply do more position changing. If I use up at least half of an hour in an hour appointment I'm good, just as long as the encounter doesn't feel rushed. Cheesy lines like 'Cum for me, baby' is suggestive of trying to rush the guy. Please refrain from saying it, because it sounds tacky and 'BP-ish'. Guys usually know when they're beyond the 'it's taking too long' point, and are probably trying to will themselves to cum. Don't aggravate the situation by throwing out the fake moans and cum for me nonsense.