When we were at Disney the first week in May we did no ADR's at all. Since there were only two of us we decided to be flexible.
On two of the day's we were at Epcot Chefs was one of the several restaurants that had seating availiable. One day we checked at Customer Service in the park at about 10 AM the other day it was even later. Both days had Chef's availiable for various seatings throughout the day.
I am not saying don't make ADR's, just saying don't sweat the details too much. Enjoy your stay and don't overplan. BTW we ate at Chef's on a prior trip with friends and had a great meal. It had kind of gotten a bad rap on service but ours was great. The food was some of the best at Disney and not overpriced for what we got IMHO.