We were there this past year. We were able to get in the MK at 4 pm. The official party starts at 7 and ended at 12, stores were open until 1, I think.
It was the best time! But plan for a down day the next day. We were exhausted!
Like Anne said, the Christmas Parade is AWESOME! and Wishes was even more spectacular. I would definitely plan to do this if you can!