I would book your ADR for 60-90 minutes prior to Wishes if at all possible. As others have said, you can hang on to your receipt and go back up to watch from the viewing deck if you want to. For me, I enjoy the fireworks if it happens while I am still enjoying my dining experience. I think the view from Main Street is a much better view so if I had an early ADR (actually - we had just that two weeks ago, a 5:30 ressie) I would finish my meal and go to the park for Wishes. However, if you can pull off the 60-90 min prior to Wishes ADR, then I'd stick with the viewing from on top of the Contemporary - it is a neat and unique experience.