OK here's a little story. When I was there in December, we were just getting off of Matterhorn when the fireworks were about to start. They had roped off the main FL area (peter pan, snow white, dumbo, etc.) but the Mad Tea Party had no line so we rode that during the fireworks. Then after the fireworks were over, they let us walk right on to Dumbo, while "lines" were forming for Peter Pan and Mr. Toad. We then got in the "line" for Peter Pan and when the main FL area was reopened, everyone walked in the "line" and we were on and off of PPF in less than 15 minutes. Mr. Toad had a walkon wait as well as Pinocchio and Snow White. I definitely recommend this time to go. Right after the fireworks!
However, as we exited Peter Pan, we could see that they had opened the castle entrance to FL and Peter Pan's line was growing quickly. I would think that Peter Pan's line is hardly ever short or a walkon, even towards park closing.