Whenever I go to Macau it's around that time, and I spend the early afternoon in a sauna. Usually it's when I'm skiving off work. Sometimes I can even do some work on my phone from the sauna
I've been to FN and Rio, haven't been to East or 18 yet. Usually there's only 5-10 girls working, mostly from Vietnam (many more turn up at around 6pm for the evening shift) so there's less choice. It depends how picky you are, but at FN or Rio you should be able to find something to your taste. However on a couple of occasions I watched someone else request a lineup, saw only 1 girl that I liked, then of course he chooses her. Do I wait for an hour for her to become available? Also do I really want to go right after that guy?
So get the lineup done quickly then relax in the lounge afterwards...
In the afternoons the lounge is much quieter, sometimes only a couple of other customers. You'll probably get more attention from the massage staff - some will aggressively sell massages, others might just come over for a chat as they're genuinely bored. I quite like that. In the evenings it gets pretty busy and loud.