Hi Faith!
Thanks for your question and for visiting the Disney Parks Moms Panel!
Same, same!! My girls and I are looking forward to a trip this October as well, and
Mickey's Not-So-Scary Halloween Party at
Magic Kingdom is a TOP priority!!
The Party is a separate, "hard ticket" event that requires an additional paid admission, and it runs from 7 PM until midnight. However, guests attending the Party can enter Magic Kingdom as early as 4 PM.
I understand your situation, and since tickets are non-transferable and non-refundable, maybe it would make more sense to wait until you arrive at
Walt Disney World to decide if you can actually attend the Party without going through the possible hassle of purchasing them too far in advance.
Certain nights do sell out, especially the closer we get to Halloween, but it might be worth the wait if you could possibly be out a few hundred dollars should your travel schedule change.
I hope this helps and I hope you are able to make it and have a SPOOKtacular visit!!
Chris