The amount of time you buy, and your stamina.
Someone in their 30s and maybe 40s can usually get off two in an hour if they get the first shot in within say, 20 minutes, then wait about 20 minutes and start in again getting the last one in in just enough time to take a quick shower and dress.
Since I'm now in my 60s, I need at least two hours for two shots, and that's on a good day.
Most gals are in the MSOG catagory. Read the reviews to be sure
That is an excellent reason to read each lady's reviews.
Now, it would be easy to say "Yes, at a certain price-point and above, that is to be expected"...... but then you might manage to pick the one provider in your area who either does not allow this, or has an up-charge for it. Or only on dates longer than an hour or only with guys named Englebert. You just never know, so my best advice is to do as much homework as possible.
Read her reviews in their entirety, and if she has recent reviews that mention multiple rounds, you might also want to PM her reviewers to ask if this was a one-hour date or longer.
Whatever you do, please don't ask her! 
Is 2 pop's the norm!??
If you are a Newbie, you should be sticking with reviewed Providers for now. In addition to what others have said, MSOG (Y, N) should be in her Profile, so you will know in advance whether it is the norm for her. As for what is the norm for ALL providers, I leave that to one of our TER statisticians to do the searches to what they find.
There are Providers who are literally "one and done" whether it's after 5 minutes or 50 minutes. They make you feel like you're just an ATM spurting some money and some juice, the faster the better. When done, they want to turn around and walk away.
There are Providers who are one-shot only but at least keep you entertained for the duration. They will sometimes offer a second shot for an extra fee.
Then, there are Providers who offer MSOG as part of their SOP. It isn't guaranteed to happen, but the possibility is there. Just to entertain the possibility of MSOG is a huge boost to the client. These are my favorite hostesses, not just because of the MSOG (which may or may not happen) but because it is indicative of their approach to the whole experience. Unrushed, caring, polite, naturally sexual, ...
By way of example, I might finish #1 early on, rest a bit and we begin round 2 but do not cross the finish line through no fault of hers. She made the effort. Other times, I might finish later yet still, with only 15 or 10 (or fewer!) minutes to go, she will offer to try for #2. I know it ain't gonna happen, she knows it ain't gonna happen but just a few minutes of extra attention is a vastly different experience from her SAYING, in words or actions, "You're done ... clean up ... get out." Just a few minutes of touching, stroking, sucking or whatever she tries sends as much of a surge to my big head as to my little head, frequently a lot MORE to my big head!
Some of my hostesses really try to make it happen and it is I who have to ask her to stop so we don't go overtime. That small effort is HUGE in my book.
To repeat: I know that #2 won't happen, she knows that #2 is a fantasy, but by playing it out she makes the whole experience MUCH much better for me
