7:00 would probably be a good time for your ADR. I'm I'm remembering correctly, when the fireworks are at nine, the water pageant comes by the Poly after the fireworks show (around 9:15). Maybe someone else can verify that. One thing you might want to consider is making a little bit later ADR and watching Wishes from Ohana. We had a 7:45 ADR once and got to watch the show from the restaurant.. they play the music in there which is pretty cool! Either way, the Poly is a great place to watch the fireworks.. have a great time!