The fireworks happen between the two Fantasmic shows. If you go to the early Fantasmic, you can get out in time to see the fireworks from the front of the park, but you won't usually be able to get close enough to see the stage show. Instead, I would get a good spot early for the fireworks. Make sure you have a good view of the stage, and enjoy the dance party. After the fireworks, everyone will bee line to the Fantasmic stadium, for the late show. As long as you don't waste time on the way, you will get a good seat in plenty of time for the show.