Fireworks crowds are amoeba-like. They aren't static. I start looking on the edge of a walkway somewhere about 30 minutes before. The crowds have a tendency to compress the closer you get to the start.
While I enjoy the show, the whole thing is stressful because of the crush of people.
For some, this is a high-stakes event, the "crowning jewel" of their visit. It's at the end of the day when many are exhausted and not in a great mood.
The bigger your group, the harder it is. No matter what you do, bring a lot of patience!