To this I always say
"I'll book you in for an hour - if I don't have any other bookings after your appointment then I can give you the opportunity to extend the booking, but if you want to be sure of having 90 mins/2hrs then you need to book and pay for that time."

There's not a lot of difference between my half hour fee and an hour but a guy turned out a while ago and I said how long are you stopping ( forgot before and at work flat) he said all cocky
"Half hour I may extend to an hour"
I just said " oh ok it doesn't work like that I'm afraid because that equates to two separate half hours , so half hour it is " 

I usually can't extend as I have another booking or I'm going out that changes their mind lol

"1 hr or maybe longer" does seem to be a "buzz word" amongst amateurish and often selfish punters with a tight spending behaviour (they earn a lot and they spend for himself or for the family but not wanting to pay more for prostitutes).

Realistically speaking, I doubt if anybody, who genuinely wanted a longer booking than an hour will be saying that AT ALL.  They pay for longer or they insist on paying more without this particular "vague" statement.  "I might pay you more" etc.  Someone said, "this is a way to make you perform better like a carrot dangling".  BINGO! I'd say.

These comments may also mean (in a wishy-washy fashion), "well, you might be attractive enough for me to keep me going"  or "let's see if I would manage much longer with you if you are GOOD or sexy" or whatever.   Read between the line, it may also mean "well, I DON'T WANNA PAY" (I put it in caps as that's quite obvious in these people who use this phrase) "I pay you for the hour but if blah blah blah, can I extend if I wanted to?" BUT THEY NEVER WILL?   Sometimes, action speaks loudest.  Personally, they don't wanna pay you more, so they are just saying.... when they do, they are not using that phrase and they are far more capable in bed and they do need a much longer time, IMPORTANTLY, THEY KNOW.   Those who use this wishy-washy phrase, they are not quite there yet.

Its not so much the length of time they ask for but the attitude.

I've had guys ask for 30 minutes /1 hour or longer and most often 1-2 hours or 2-3 hours. The second bunch are always TWs, when I say I only see,new,guys for an hour they usually give themselves away with some other TW shit and never show.

On the other hand some of the first bunch do extend, its just they are not sure how they'll click. However I always factor in only the shorter request, if it suits me I will extend. If I get another firm appointment then tough luck on them!

I once had a client who would book a particular length, then always ask for a longer time when he arrived. Combined with other difficult behaviour it felt like part of some sort of controlling puppet game, he wasn't prepared to change his behaviours when asked so I told him I wouldn't accept another booking from him.

If a client asks if he can potentially extend, I tell him to bring the cash for the full extended time. Cash goes on the side and then we crack on. When he's done, I check the time, and remove the correct fee returning any excess.

I started that after a couple of clients shorted me the excess time by suddenly realising they'd forgotten their extra fee.

I get quite a few first timers and bdsm clients, the first group aren't sure how long they can go for. The second group aren't sure how long I can go for. I don't see a lot of clients so I don't mind extending, but I always insist on seeing the full potential fee upfront. I'm not stopping every 30 minutes to ask the client to top up the pay.