Last year, Christmas Eve day was very busy, but manageable, utilizing FP. In the evening, from 9pm to Midnight, nearly everything in FL was walk-on. DCA closed at 9pm last year, so we hopped from there to DL at that time. We noticed a lot of people left the parks at that time.
Christmas day was quiet until 11am, then the esplanade was bursting to the seams. All the bag check lines were backed up to the shuttle bus drop off area. Probably took 40-45min to get inside DL. At that point, you couldn't move down Main St because of the congestion. We turned around and left and hopped over to DCA, where it was much more manageable. We tried several times that day to meet up with friends in DL, but it was just far too crowded for our liking.
Of course, this year who knows how Carsland & BVS will affect the crowds in DCA. Plus, hours have still not been updated for Christmas week....but, I would venture to guess that DCA will be open much later than last year. Keep in mind, too, that for our party, Christmas Eve and Christmas Day were our last days in the park. We had already spent 4 full days in the parks (out of 6 total) and we were using those two days just to soak up the ambiance and enjoy the festivities.