What time of the year are you going? It will make a difference for crowd sizes and line-up times.
And what show are you looking to see? First in the morning? Last in the day?
In general, 20-30 minutes for all but Fantasmic.. I would give that one about 45 minutes to an hour for up front seats.
Whenever I have seen Nemo, B&TB, and FOTLK, they've always been letting in up to show time. (Never full). Fantasmic is always a madhouse. Although I have never been to the second seating for Fantasmic, it may be different.