It is one way to know that it was a great session.

If things don’t click, it doesn’t mean the lady is at fault bc sometimes, as you mentioned, the chemistry just isn’t there. Not everyone is going to be a perfect match. But I believe that is where experience comes into play, ideally even before reaching out to someone for a date.
.
Most experienced guys would probably agree that when you do your due diligence, the chances of having a disappointing date drop significantly. Early on, when I was just starting out and lacked that insight, every date felt like a gamble. It got to the point where I almost walked away from the lifestyle entirely. Back then, I was relying solely on photos which is something I quickly realized was incredibly risky, both legally and compatibility wise.  
.
Fortunately, I had someone with experience take me under their wing and show me how to properly vet potential dates. That guidance made all the difference. These days, I rarely have a bad date, and like you said, the time tends to fly by, and at warp speed, for the best of them! lol

The young lady could leave when the time is up, leaving the guy, all googlie eyed.
So the better question is.
Ladies,“ Ever lose track of time with him”