I have heard sometimes if they are ready they start letting in about 3:45 or so, but usually no later than 4. Was just there on Sunday and breezed in at 4:10 (waited forever for a bus at Saratoga) but the lines were really short and we got in quickly. The party entrance is on the right side, regular turnstiles on the left. Make sure you get your bag and party wristband when you come in!