Every time I go there is usually 1 girl worth taking in the backroom. Sadly there is often only the 1. Your standards may vary.
OTOH I've never been miscounted, every girl seem to offer the same level of service, no door fees, bathroom beggers, coat check etc. I've never been offered extras either but I am just looking to get my hands on some T&A so I am OK with that.
As I understand it, really late on Friday and Saturdays are the time to go, I have not been there that late recently but I guess after 10 or 11.
I have not been for about 6 months.