I have the same experience as longtimedisneylurker - we're always there at busy times like holiday seasons, and so Carnation is open for dinner when we're there. In fact, one time we even went there on a cold December night to get dessert only (and coffee), and it was while the holiday parade was happening. When we exited Carnation, we hit Main Street at the exact moment the snow was falling - which was magical!!
One time - before I began making reservations for CC - we had to wait in an almost 45-minute line to get a table. I guess a benefit to going at less crowded times would be that the wait to be seated is much shorter but the restaurant closes early.