It's starting to sound like a broken record around here but I also have to say late at night, particularly after all the entertainment is over. I love the emptiness that results from the mass exodus after Fantasmic and the fireworks. I adore the feeling that any attraction is possible.
In particular, Christmastime is extra special to me. When you can hear the beautiful music paired with the sparkle of the lights, it takes everything I have to keep the happy tears from flowing.