When an evening is full
Seats are split evenly between women and men. If your side is full, you go on that evening's waitlist.
Every evening has the same number of seats for women and men, so everyone has someone to talk to in each round. The first evening has 10 seats on each side.
If your side is already full when you book, you go on that evening's waitlist. Booking, and the waitlist, are free.