I would say that most people plan their meals 180 days in advance or as soon as they book their trip if less than 180 days-especially if you are traveling during a busy time- which you are now. The great thing about that is that you can always cancel if you will not use your ADR.
I just got back from Disney on Monday and we had a heck of a time finding food in the World Showcase at Epcot. Everything was booked so we just ate at Japan’s counter service place.
Another suggestion is to walk up to the restaurant at opening which is usually 530pm and try to get in then. They can usually accomodate you- especially Cape May. We have walked in there many times with out an ADR and were seated within minutes.
Another place you can usually get into without reservations is Trails End at Fort Wilderness campground. Great Buffet!
Unfortunately, Disney is so busy and their restaurants so popular that you don’t have much of a chance without and ADR. Book them for your next trip and just cancel if you can’t make it. I always book one ADR a day just so we have a place to eat.