They are a must at any time and as far out as you can get them if you want a popular restaurant (Le Cellier, CRT, Chef Mickey's, California Grill within 2 hours of the fireworks, possibly Coral Reef). They are probably a very good idea to have prior to your trip if you want character meals or buffets. Anything else I would suggest an ADR one or two days before you want to eat. These may be much more difficult to get if you are traveling at peak attendance seasons or if you want peak mealtimes. Because this is on the dining plan board, I assume you are looking for restaurants that accept the dining plan. I personally try to limit attempts at walk-in dining (no ADR at all) to establishments that don't participate in the dining plan.