It will be pretty crowded, but lining up 2 hours before shows is a bit much. And hour MAYBE an hour 15 minutes before shows at most. Yes, the park may close due to capacity but that wouldn't happen until late night. And yes, there will be a fireworks show. Its worth a day. But if you happen to have two days at Seaworld, it may be better to do half a day (Morning to afternoon) one day and the 2nd day (Afternoon to evening) the next.