Hi there, Paul!
As a planner, I like to know what's going on at
Walt Disney World. It will be about 180 days in advance when the
theme park calendars are available, and dates for
Mickey's Not So Scary Halloween Party have historically been released sometime in the spring.
Based on years past, the party usually happens on Sundays, Tuesdays, Thursdays, and Fridays. This far in advance, the days are subject to change, but these days have been pretty consistent over the past few years.
If you can make it work during your stay, I highly recommend the festivities at Mickey's Not So Scary Halloween Party. The tickets sold are limited in number, so wait times for most of the attractions are shorter than you might find them during the normal theme park day. As an example, my daughter rode
Seven Dwarfs Mine Train twice in a half hour during a recent party. We saw day time waits as long as 90 minutes for one ride. There is also special entertainment, parades, and fireworks that you won't see during a regular theme park day, plus the parties usually feature rare characters. In years past, we've seen all seven dwarfs, the Gravediggers from the Haunted Mansion, and more! Oh - and candy - did I mention candy? You'll need an extra bag to go home with it all if you decide to hit the trick or treat stations!
Whatever you decide, enjoy a wonderful holiday, Paul.
Anna