Hi Lynn,
Mickey's Not-So-Scary Halloween Party is a special event a Magic Kingdom that requires a separate ticket. Details for 2013 have not been released, but, historically, the party has lasted from 7 p.m. to midnight on select nights in September and October.Usually, guests with party tickets are admitted before 7 p.m., even as early as 4 p.m.
So, if you want spend the earlier part of the day at Magic Kingdom, you will need a regular park ticket or pass. After 7, those without party tickets will be asked to exit the park.
If you plan to do the party, which I recommend, my suggestion would be to spend the day at another park or use that time to relax at the resort pool. You want to have enough energy to enjoy every minute of the party and its special parades, shows, fireworks and treats.
Please let me know if I can answer any other questions as you plan your vacation. October also is the month for the Epcot International Food and Wine Festival, one of my favorite Disney activities.
Enjoy your visit!
Wilma