We just had a 5pm ADR at Ohana's, got seated 10 minutes late. We made it to Main street for the parade at 6:50pm, but I felt rushed, no time to relax and enjoy dessert, just gobbled it down and dashed out. I would have been happier with about 15 minutes more... I'd try for an earlier ADR, or as others have suggested, watch from the beach.
The boat goes directly to the Poly, so you can watch from there, they definitely pipe the music into the Poly's beach.