Hi Stephanie!
Mickey's Very Merry Christmas Party is such a wonderful event! Celebrating the beauty and joy of the Christmas Season is absolutely the BEST on Main Street, U.S.A. in the Magic Kingdom!
Traditionally, the crowds are not high during the earlier parties, including the very first one. I have noticed that the crowds are usually higher on weekends and the closer you get to the actual holidays, Christmas and New Year's. You will most likely find that you will not have to wait more than 15 to 20 minutes for
most attractions.
The schedule is available the day of the event. However, you can expect the festivities to begin at 7:00 p.m., with the parades taking place usually around 8:15 p.m. and 10:30 p.m. The Holiday Wishes Fireworks show is usually around 9:30 p.m. The times are subject to change.
I recommend you obtain one of the schedules earlier during the day to plan accordingly. These are found near the Main Entrance of the Magic Kingdom, at Guest Relations, and at most of the retail stores throughout the Park.
I hope you have a fantastic time at this joyful event in Disney's Magic Kingdom!