Personally, I would do it your first night there because then you are able to view it another night IF they cancel the show. Also, 2 hours isn't bad. Potty before sitting down, snacks, card games and some paper with crayons work wonders!! I did it with two 6 year olds who were constantly bickering, another time with two 2 year olds who were grumpy and whiny, once with 2 adults (me and a friend-and the friend complained more than the kids had!!! LOL) and another time with my 2 yr. old AND my 6 yr. old. One of those giant turkey legs kept them busy for almost an hour alone because they love chicken legs and were just amazed at how big that turkey was. HAHAHA
Have fun, relax and if you don't get the greatest spots, oh well. The fireworks are awesome either way, I am sure.