The rough itinerary is for people to arrive around 7pm, grab a drink and have a think as to what you would like to play. Groups will start forming around quarter past. Latecomers can join an existing group or form a new one. Most of the games are fairly short so you wont be waiting long to join and there's plenty of quick 'filler' games available to keep you entertained in the meantime.
For more info, see the About Us bit. RSVP encouraged but not demanded.