I don't think you need to make ressies very far in advance for any CityWalk restaurant -- EXCEPT Emeril's, in which case months in advance is probably not too soon.
The only exception I can think of is Margaritaville around the time Jimmy Buffett is expected in Orlando. he has a way of dropping in when he's in town. And I do believe he's scheduled to play one of the big arenas downtown in the near future. Anyone know the exact dayes?