After you make the reservation online you can call to have the main dining line process the refund ASAP and don't need to wait to get there. I just did it today.
Also the AP discount is for the 4 and 8:30 seatings for all categories. The 6:15 seating is for sure not discounted on Category 1 but I'm not entirely sure about 2 or 3, since I purchased Category 1.