Hi Rebecca,
I absolutely love
Mickey's Not-So-Scary Halloween Party. My husband and I took our boys last year and it was the highlight of our vacation! I completely understand the need to plan. It's hard to wait for those dates!
I looked back through my emails to see when I purchased my tickets and it was in the month of May. As of now, I don't have any information about when the party dates might be released, but I suggest keeping an eye on the
Disney Parks Blog. They do a great job of getting information out as soon as possible.
In the meantime, I would go ahead and make your dining reservations. Last year, the September dates for Mickey's Not-So-Scary Halloween Party fell on either Sundays, Tuesdays, or Thursdays. There is no guarantee that this year will follow the same pattern, but if you have a must-do experience to schedule, it wouldn't hurt to avoid those days when making your reservations.
Please let me know if you have any other questions, Rebecca. Wishing you a boo-tiful vacation!