Christmas is great at AK! Make sure you are there during day to see the Merry Menagerie! Then at night the decorations are beautiful, my second favorite park for Christmas.
Most are in front by stores and Tree of Life, but also different holiday decor around Africa, Asia and even some in Pandora.
Then the Tree of Life has some shows on it, starting at dark.
We were there last December and AK was really special. I would plan to get there around 2 maybe? Enough to time to see Merry Menagerie, browse shops, eat, walk and see all decor as it turns dark. And stay until close, which is around 6 because we were there same time you are going.
Have fun!