well i don t see why you would want to waste the money and day on your ticket to only go for a couple of hours in the first place. and there is no way you will get in even at 10pm cuz between dec 21st and jan 1st is the busiest time of the entire year and many days especially from xmas day thru new years eve the parks fill to capacity buy noon at the latest and everyone plans on staying the entire day since it is open so late. if you want to go to magic kingdom on the 27th you will need to get there before the park opens to ensure that you get in.
the reason that the park is opened so late is because December 27th is right in the middle of the busiest week of the year. If you arrive at ten I can almost guarantee that the park will have reached its full capacity which means you can t get in unless your staying at a disney resort (unless they changed the rule)
The parks take turns having late night hours during the year but this is ONLY for guests of the Disney hotels.. My husband anddaughter would take me and the younger kids back to the room then go to whatever park was open late for a daddy daughter date.
Usually around that time they either have fireworks or a parade on Main St which in past years around that time is very packed. Some people go home after the fireworks or parade so if you can come after would probably be better.