They closed at 6:00 this last December (we were there both CM days). They showed the fireworks right at 6:00 if I remember correctly (which was great considering we have little ones) and then everyone filed out down Main Street...little bit of a nightmare exiting! The crowds were not bad at all those two days earlier in the day, pretty low waits on everything we went on, but leaving the park (literally at a snail's pace) after the fireworks was something I had never experienced...we've never been to DL at crazy busy times though. I had never seen so many people trying to get out at the same time!
All that to say...we loved going that week! It was before most everyone's Christmas break and we were able to do so much in the 3 days we were there (Sun-Tues).