This is about right. You can usually judge how popular a Prom will be by whether the seated tickets are sold out. If there's still plenty of seats left (check o

This is about right. You can usually judge how popular a Prom will be by whether the seated tickets are sold out. If there's still plenty of seats left (check online), then it will most likely be a short queue for standing tickets. If the performance is otherwise a sellout, then I'd try to arrive a minimum of 1 hour prior to stand a chance. One doesn't have to stand the entire time either. Plenty of people do sit around the edges, and almost everyone does during interval. The advice to bring a blanket to sit on is good.