Some events publish guest list rules. They appear on the event page above the join form and in your confirmation email, and they are worth reading before you head out.
Women arrive by / Men arrive by
These are arrival cutoffs. Arrive before the time shown for you — after it, the door team is warned that you are late and may not honour the guest list. The door scanner flags late arrivals automatically, so turning up past your cutoff is never a technicality that slips through.
Dress code
What the venue expects you to wear. If the door enforces it strictly, the event page is where you would have been told.
House rules
Anything else the venue wants you to know — table etiquette, ID, re-entry and the like.