I walked into the MK at about 9am Christmas day this past year, and it was already pretty mobbed. Line all the way down the street for the bakery. 45 minute wait for Cosmic Ray's counter service breakfast. Eat breakfast before you go at least, if you insist on going that day. But most people I talked to who went said they got in maybe 3 big attractions the whole day. Fast passes for Space Mountain for 7 hours later (and this is in the morning, and the ticket says no fastpasses for 3 more hours). I mean pretty absurd. The only saving grace was, after the first Spectromagic and fireworks, the park did clear out, and by staying until park close at midnight, I was able to do 5 or 6 attractions in those last two hours between 10 and 12, whereas I did maybe 3 attractions between 9 am and 10 pm. And, there was a final show in front of the castle at 11pm that wasn't crowded, so that was nice too. Even though it is special to be there on Christmas day and see the Christmas parade on Christmas day, I'm starting to think it's not worth it to be there during the daytime hours that day, at least not if it's that bad. My suggestion: skip the morning and afternoon at MK, and just go for the fireworks and second Spectromagic, and then you can ride all the attractions you want to during those late hours before closing. Oh and by the way, Christmas day fell on a usual extra magic hour day for the MK, but to reduce crowds they switched the days with another park for that day. I don't know if they still let people in early, because I wasn't there quite that early (9am to 12 midnight was a long enough park day for me), but the schedules they gave out at the resorts showed the switch for extra magic hour.
