Dude,
It usually opens doors at midnight and its begins to fill pretty quickly from there.....
Bigmc's idea is a good one. the queue at about 2-2.30 is usually a fair size but they get them in quickly. The residents play from 12 so if you wanna see them then get in early....(Vicky Devine and Alex Ellenger....Go see Vicky if your into your trance, her warm up set is perfect for that time....plus she's a mate so i gotta advise that!!)
Big names dont usually go on til about 2ish. If you take on Bigmc's idea, check around the club for the small posters they put up with all the DJ's set times.....then you know whats best if your goin to see anyone in particular.
Hope that helps..
Luigi