"It is my absolute pleasure to inform you that your screening is now completed! She does prefer to share a longer engagement with new friends, of 90 minutes or longer if that might work for you. If not, please let me know what date and time would work best for you, and how much time you were wanting to share, and it would be my pleasure to arrange it for you!"

when reviewing most providers websites. Unless that extra 30 minutes is otc in order to have that longer engagement which she so desires, I select the appropriate timeframe that fits my needs which is 1 hour, especially for the 1st time meeting a new provider.  

I’ve seen ads or websites from many providers that say they prefer 90 minutes for a first date, and their reviews are clear they’re up for MSOG regardless of duration.  

But common sense suggests that if you book longer appointments, you will have a better luck at going multiple times.  

De jure and de facto recently came up in a different context. But here's what I mean ... There is de jure "MSOG" and there is de facto "No MSOG."  Let there be de jure MSOG even though, for many of us, there is de facto no MSOG.  
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Except for the most naive newbie or stingiest clock watcher, nobody should expect MSOG with just a few minutes left on the clock. "But we've still got 2 minutes! I want my full hour!" Forget about it.  
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HOWEVER, I think it goes a long, long way, at least with me it does, if my hostess offers or suggests that we go for another pop with a reasonable amount of time left, maybe as little as 20 or even 15 minutes ... or even 10 min! I know I won't be able to finish (de facto no MSOG), SHE knows I won't be able to finish but even the smallest of effort, de jure MSOG allowed, really makes me feel great! I will usually tell her to stop and that it is highly appreciated and thank her for her effort (and the compliment!) but we can pick up where we're leaving off the next time.  
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On the other hand, an early first pop followed by "too bad, one and done" is a huge downer.  
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A hostess who at least makes an effort really wins my appreciation in many ways.

of now long it took you to get the first pop, and how much time is left of the session you booked.  If you booked an hour and you get your first pop after the 40-minute mark, its unlikely that she will let you go for two.  Likewise, using the "time-left", calculation, booking 90-minutes does not automatically get you two shots either.  If it takes you over an hour to finish the first one, and there is less than 30 minutes left, . . . . . just do the math.  This is why I most often book 2 hours.  I got to a point where I didn't finish the first round until the 50-55-minute mark, so 90 minutes total was not going to be enough time to go again.  

I get what you're saying pertaining to time.  Understand, I am not a marathon man.  Usually the visuals, rhythm, excitement, etc. gets the best of me and I have my first pop within the first 15 to 20 mins of the session.  The ($600/hr) provider I am referring to, that session went much the same as she was super hot, so I got the hint that MSOG was a 90 min session.  All things considered, I still can't see knowingly dropping 500/600 for a none MSOG provider.  

more time left in the session than you have already used for the first pop, even in an hour session, the provider should be willing to allow a second cup.  It SHOULD be all about time used versus time left on the clock.  

Absolutely since most claim you are paying for my time not activities.  LOL

And just to emphasize my own point of view ...

Very true. I allow second cups, actually welcome them, but I can not guarantee it. That is on you and jr