This is the info off of Deb's
When you call to order your dinner package tickets, you will be asked to select a restaurant and priority seating time.
According to WDW Dine: For the 5:00pm show, you should make your dinner pririty seatings for 7:00 or later; For the 6:45 show, you should make dinner priority seatings for 4:45 or 8:45; For the 8:15 show, you should make dinner priority seatings no later than 6:15.
Be sure to allow sufficient time to dine and get to the back of World Showcase. I recall year before last having a 5:30 priority seating at Le Cellier for the 8:15 show. For whatever reason, we weren't seated at Le Cellier til 6:00pm and then at 8:05 had to run (just about) to the American Gardens theatre to catch the show. The "reserved" seating area had already been opened up to non package guests.