Hello Andrea! Welcome to the Disney Parks Moms Panel.
My family and I celebrated the beginning of our evening before
Mickey's Not So Scary Halloween Party by securing Advanced Dining Reservations for
Be Our Guest Restaurant.
Since Cast Members usually allow Guests to enter Magic Kingdom a little earlier than the 7pm starting time for
Mickey's Very Merry Christmas Party, we made Advanced Dining Reservations for 5:45pm to ensure that we didn't miss out on too many of the festivities. With your 7pm
Advanced Dining Reservations at Cinderella's Royal Table, you are generally requested to arrive 15 minutes before your scheduled time.
While a Cast Member cannot guarantee that an early arrival will mean earlier seating than your scheduled 7pm Advanced Dining Reservations, Cast Members at Walt Disney World Resort always do what they can to accommodate Guests requests.
My first tactic would be to try to secure Advanced Dining Reservations for earlier in the evening at Cinderella's Royal Table. Using the early access to Magic Kingdom means you may be able to finish your dinner before Mickey's Very Merry Christmas Party even begins. If you are unable to get an earlier time, arrive as early as you are comfortable at Cinderella's Royal Table (within reason) with the understanding that you may still have to wait if tables are not available.
Have a Very Merry Visit!
~Todd