My guess is you'll get an hour less time. If you go at 2:30am and spend an hour, now it's still 2:30am and my guess is she's leaving. That'll be the most expensive 0 minutes of your life!
Mathematically, let's say she was $300/hr. That's $300/0 so you effectively paid her a number approaching infinity dollars per hour. So, you're better off to go for 2+ hours. She may give you a better price for a longer visit, but even if she doesn't, $600/1 is only $600/hr (on the clock vs actual time elapsed). It's a better deal, and she'll probably appreciate it more too, for future rewards.
Well. . . never thought I'd break out the calculus on this forum, but there we go