Some of you are making this sound more complicated than it is. 1) You reserve on dayuse.com, 2) when checking in at the front desk you say "it's dayuse" and 3) from there it's like any other hotel checkin. You provide ID, a card for them to charge security, and they give you the key cards. At that point it's no different than if you booked for the night. Guests come and go, and so can you and your girl.
Dayuse has an option to prepay and to create an account, I've never done either.
One thing I do, like Perfecto, I ride the elevator down and when it hits "L", I have them jump right on, because a lot of these hotels have only 2 elevators for many floors and the staff - housekeeping, maintenance , etc. - often have to commandeer one of them, and they start to run like the L train at 8:45 AM.
I've yet to stay in a fleabag place, these are all mostly Hilton/Marriot/etc..