The characters do pop up every now and then but as PP mentioned, nothing you can count on or even know about in advance. I know we happened upon Tiana at POFQ one time, or was it at POR. I forget now, we stay at both so often. At any rate, we came back via the bus and she was in the lobby. Unscheduled and unannounced. I've read of them being at other resorts too but it's not at all common.