While the party doesn't officially start until 7, most party things will be available long before 7 (for those who have checked in). Last year we had a 3:30 LTT dinner which worked out perfectly. After dinner, we checked in for the party, got on line for Moana, saw Moana, got our party merch on MSUSA, did some of the Magic shots on MSUSA, walked the cut through behind MSUSA and got on line for Lotso well before 7 (and were finished with our Lotso M&G by 7:05). Long story short, don't waste valuable pre-party party time on an ADR. You are better off with a late lunch or early dinner and then enjoying some of the party exclusive food items later in the night.