Jan:
In the past, the Hallowishes Fireworks began at 9:30 p.m. for
Mickey's Not So Scary Halloween Party. I have not seen anything posted on the Disney website that would indicate anything differently for this year's party.
Usually, a meal at the Polynesian's 'Ohana restaurant would take our family about an hour to an hour and 15 minutes, a little shorter than other restaurants because of the family-style dining. However, the wait to be seated can vary greatly, especially because your reservation is not at 5:00 p.m. when the restaurant opens. If I were you, I'd let the hostess know that you'd like a window table, if possible, when you arrive for dinner. They won't be able to guarantee it but if you're willing to wait, it doesn't hurt to ask. You'll probably time the fireworks to enjoy them near dessert.
If you are seated quickly and finish your dinner before the fireworks begin and feel awkward waiting on them, know that you can slip down to the Polynesian's beach area to see the fireworks. I actually prefer this view to the restaurant's.
Wishing y'all a magical vacation!
Whitney