That probably means there are two F! shows: one at 9; and one at 10:30. That would be the norm. The fireworks begin immediately after the end of the first F!, and the second F! begins about 50 minutes after the end of the fireworks.
(EDIT) Actually, we're there at the end of September, too. (Duh, I'm an idiot.) Sunday 9/28 has two F! shows, one at 9, one at 10:30. So you can see both F! and the fireworks if you want (if your little one can take the noise.) Just make your way to the second F! after the fireworks. It's pretty easy to do since you have so much time to make it to the Rivers of America. (We did just that a few weeks ago.)