Lots of questions to be asked about the technical and logistical elements of the show being run during HHN that could make it more difficult than one could imagine to do the show earlier. But usually when dealing with light you can't control and projectors outside, the later whatever it is that is happening, the better.
But, the reason the show probably starts that late is because HHN is a late start event and they want you to spend as much time in the parks as possible. I don't think this is something they would plan as a distraction or diversion.