Well, the Cast information is conflicting on this one... It says:
Dinner Shows: All shows can be confirmed for all dates through 12/31/06. Bookings for 1/1/07 and beyond can be confirmed 180 days prior to the requested dining date
But it also says...
Dinner Shows
Resort guests may make reservations when they arrange their room accommodations. Dinner show reservations are available up to two years in advance. Payment in full will be required at time of booking for the Hoop-Dee-Doo Musical Revue, Disney's Spirit of Aloha Dinner Show, and Mickey's Backyard BBQ. Guests may cancel up to 48 hours in advance to receive a full refund.
Perhaps you should call anyway just to verify...