Until the end of next week the DL is open until 8pm, so the fireworks will go off at 7:45pm.
After next week, the park stays open until midnight up to Thanksgiving, goes back to 8pm for the next few weeks, then back to midnight Christmas week until Jan 2nd or 3rd.
I'm there Dec 3rd-5th and the park closes at 6 on the 5th . I don't know if it's for a special event or what.
(Actually, last time I was in the park on a special event day, we just kept wandering around well after closing announcements. I remember walking past Indy and there were CMs posted out front. We asked if they were open and they said "come on in." We stayed riding e-tickets with no line for at least an hour after close.)