Try to get the first pop by 20-25 minutes, then have 10 mins chat, and start the second round no later than 35 minutes. (I use a timed playlist to help me stay on schedule without looking at my watch.) Get the second round started by putting your hand on his cock and saying "So, are we going to get a round 2 do you think?" If he feels up for a second round he will respond positively, if he's done for the day he'll often get up and leave at this point.

The reality is that they 'want' and what they're physically capable of may very well be worlds apart and not something you (or they!) will be able to dictate, guarantee or have much real control over.

This is very true! I've had loads of guys ask me "Can I cum twice in an hour" and I always say "Sure if you can manage it!"

Then they cum, give it 10 mins chat and say "Do you know what, I'm done, you've drained my balls too thoroughly"

Yea, the first cum has to be a fuck unless you know you can suck the life out of them with your bj skills.
Have a chat. If they don't think they can manage they usually mention during the chat that they cannot manage a second and either end the meet, or carry on chatting.
If they can or haven't said anything, start stroking his cock. He will soon let you know.

Be wary of the time. One of my regulars can fuck easily non-stop for 40 minutes. The second cum with him in the hour is not possible.  The first comms with him was about the 2nd cum. The first time we met, we fucked for ages. Had a break and he wanted to go again with 5 minutes left. Obviously wasn't going to happen.

Another one can cum 3 times within the hour. He fucks very, very quick. Have a break. Oral and he cums quick. A quick break and a quick fuck. He's not in a relationship so he either saves it for me or has a wank lol. And we still have about 15 minutes left.

When I was working regularly it always used to amuse me the boasts Id get pre sex about staying power, multiple orgasms and making women cum several times. I’d play along with it but you knew it was ball**** most of the time! I’d say at least 60% of clients wouldn’t manage it a 2nd time. Some you’d only have to stroke or roll a rubber on and they’d spill! Then you’d get the excuses, “it doesn’t usually happen to me, that’s first time”, etc, etc, yawn!!

Or after sex I’d be lying there and deliberately ask him if he’d be ready to go again, knowing he was as flat and deflated as a puncture on my mountain bike! Then again the lame excuses followed causing me to give him a “you can’t can you, another hot air punter” !

It's rare I see anyone who climaxes twice in one hour, even 90 minutes and multi hour bookings.

I'm interested are the people the OP sees specifically asking for 2 orgasms, or are they simply enquiring about any cum limits?

Do wish these clients would have better memories about their performance.
Oh can I Cum twice in half hour,?
 I always ask do you usually have a Cum twice in half hour with an Escort? to which they either go silent or say yes and not turn up.!
Then there's the ones who shoot fast and and Cum a tiny bit of second time after excess wanking with your hand or theirs  and are self conscious about the performance

If they ask me if they can cum twice in 30 mins /1hr
  I reply with  “I don’t know can you “ 😂

 I mean am I supposed to be a bloody mindreader as well as a hooker and know if they can cum twice in a certain amount of time

It's rare I see anyone who climaxes twice in one hour, even 90 minutes and multi hour bookings.

I'm interested are the people the OP sees specifically asking for 2 orgasms, or are they simply enquiring about any cum limits?

Both really. Those who’d  boast they were some type of stud and could go all night, only to cum quickly. (I’d look at them as we commenced and think “really”? Knowing  full well they were talking talking c**p, then the others who’d ask if they could climax in me multiple times in the booking time.

I’d reply politely yes if they were able to but the vast majority couldn’t. Most accepted defeat but it was also amusing and annoying at the same time guys whod try and fumble away trying to get back inside you without being hard enough or fail at the first point when you to tried to roll a durex over half deflated cock. I’d try and hint the little fella wasn’t going to play, even with few encouraging stokes. Got wise to it as it was a waste of my condoms! After so long would be “time up, have to go, another booking sweetie”!

Now I’m semi retired and just have regulars I know their limits. Have the odd quick cum accident with one particular gent but as a rule I know their limitations. There is one particular guy who can cum twice. He can make me orgasm too which is always a nice bonus!