we did the 5pm show last year. It was still light at the beginning but was dusk/almost full dark by the time it ended. (This was on 12/21) We had a FP for Frozen that started at 5:40 and we were out of the show and able to check in for that right when the time window opened. We still lined up almost an hour ahead of time (did a "lunch" at Rose and Crown around 2:30ish) and were in front of Japan, so not near the front but not too terribly far away. I picked 5pm on purpose because I wanted to be finished with it and have plenty of time to do other things in the park and not risk hearing part of the show while waiting and ruin the experience.
CP is a one and done for us. It was nice, but I didn't find the dining package to be a good value at all (especially not at Rose and Crown, but it's what the rest of my family wanted), although it was nice to have the guaranteed seating. If we ever see it again it will be standing outside of the theater.
If you want to see it in full dark, you'll want the second or third showing. I don't feel our experience was diminished by the time slot, though.