I've posted about this before but I go about once a month because I like the facilities there, and prefer to go in the afternoon when you're more likely to get the swimming pool or even one of your jacuzzis to yourself for a fair chunk of time. I have stayed on in the evening sometimes and it varies enormously, Friday and Saturday's are likely to be when it's busiest but that hasn't always been the case (with one hot Sunday afternoon in the summer being the busiest I've ever seen it). As for male / female ratio, again it can vary, but I'd say it's at the very least five guys for every woman, and sometimes it can be far bigger, and most females are there as part of a couple.
I do feel like I should stress again that you can never predict what it's like (the first time I ever went there three amazingly hot black women in their twenties who turned up without male partners) but it's very rare that I've seen a guy pull someone they've never met before there, and if they do they tend to be young, extremely fit, and quite happy to fuck someone who's thirty or forty years older than they are.