Mickey's Very Merry Christmas Party is a hard ticket event, so regular theme park admission is not required. People have been talking about being allowed into the Magic Kingdom at 4:00pm with their MVMCP tickets, so you may actually be able to squeeze in a couple of extra hours.
Thanks... that is what I thought. I am using park-hopper this trip so I think that will be a themepark "off " day for us. Just wanted to make sure though!!