When she sets her clock in the room 15 minutes ahead  and you don't realize it until you check your phone after you leave.

 
This used to happen to me more than I care to remember, but fortunately not so much now-a-days.

 
Other than that, it's when you are immensely enjoying the session for whatever reasons, and that fortunately, is much more the norm now.

Time flies when you don’t notice the time during the session. This is why a clock watcher kills the mood. All attention needs to be between the provider and client. While I understand a provider doesn’t want her time taken advantage of, she just needs to be discrete about it.

 
Obviously, there are other factors in play. But I would argue, the moment a client isn’t enjoying anything about the session, fair chance he’s counting the minutes in his head. My less stellar sessions are often ones where I get off and book it, only to realize I left 20-30 minutes early. Meanwhile, the minutes were less enjoyable so it still felt like an hour.

 
The goal is when it’s over to feel like you haven’t been there that long. When a client doesn’t realize the time, he’s more likely to return and book a longer session. I have had a few sessions where time flew by so fast I regretted not booking a longer session with said provider.

One provider I saw really made the time fly.

She turned the clock ahead while I was in the shower.

time doesn't fly; it vanishes like it owes me money.

 
A great date makes time melt. A bad one makes you rehearse your escape plan.

 
A great date?  Connection, comfortability, and that little spark of chemistry that makes time misbehave.

I've been with a few duos where the interaction between them was so intense I lost myself in enjoying the visual feast.  The good news is that, when that happens I'm so turned on that I don't need a whole lot of time doing the deed in order to pop.  When two women are really into it, an hour goes by for me like a wisp of smoke.

I do research on the ladies to make sure (or as close as possible) we are compatible based on my personal liking from TER, P411 profile, their website, communications, etc...  E.g. I brought a unique beverage of choice one lady mentioned in her profile. Another lady was an alum many years apart (not from her profile, but while during screening communications . Time flies and we usually go past our meeting duration...