Why don't you just talk to the ML you want to book and ask her how she wants to be compensated for something like that?

Personally, I can't imagine what I would do with anything more than 1 hour in a massage parlour. You're talking about tipping the girl in room, so it can't be a Korean parlour where you can have a nice big room with comfy couches, bed, hot tub, etc. The tips are included upfront in those K places. I can see myself spending an extended amount of time there cos it's comfy, great for lounging around, cuddling on the bed, etc.

With a normal massage place that you're referring to, it's just 4 walls, a massage table and maybe a small shelf. You can't get comfy, certainly she won't be comfy either... The room is simply not suitable for long stays. Not to mention boring as hell!

If I really liked an ML/WL and wanted to spend more time with her, I'd be asking her for some sort of "compensated dating" arrangement and get out of that room, that's what I'll do.