We just ate at the Play and Dine breakfast at Hollywood and Vine at Disney MGM studios on Tuesday. Our reservations were for 11:15 and I asked the server when we were seated how long the breakfast buffet would last. She said that they would keep replenishing it for quite a while, and that when the lunch food started to go out on the buffet we could also eat that, too. Sure enough, the breakfast food was fresh, and we were also able to try a few tastes of the lunch buffet.
BTW, if your kids like Playhouse Disney (especially Little Einsteins and JoJo's Circus) Play and Dine is a great experience.