Welcome back to the Disney Parks Moms Panel, Christy!
How fun you have plans to attend Mickey's Not So Scary Halloween Party on Halloween! I can't think of a better place to be than the Magic Kingdom!
Yes! You will be able to pre-book your three FastPass+ selections for Magic Kingdom beginning at 4pm. However, based on FastPass+ demand for that day, you may not be able to get all three selections in between the hours of 4pm-7pm. Additionally, entry into Magic Kingdom for Mickey's Not So Scary Halloween Party is not always guaranteed at 4pm--early entry is contingent upon crowd levels and party ticket sales, keep that in mind as you plan your day.
I also want to let you know about some recent
enhancements to the FastPass+ system that may help you plan. You are now able to secure additional FastPass+ options once you've used your initial three, or the return time window has expired. These additional FastPass+ selections may be made one at a time at any FastPass+ Kiosks inside the park with the attraction you wish to ride. This would allow you to utilize three FastPass+ attractions at Epcot and then select more FastPass+'s once you get to Magic Kingdom. Just another option to consider.
I hope this information is helpful, Christy! Please do not hesitate to ask any additional questions you may have. We are here to help!
Happy Planning!
Faith D.