You can really show up at any time. The lines will start at the bag check, but after you get through the bag check you will still be waiting in line at the gates. We usually aim to hit the bag check area at around 6:40 on a 7:00 early entry day. There are always people who have been there before that. I think the earliest I have ever arrived was about 6:20 and there was already a couple dozen people waiting.