The River Belle Premium packages run out the fastest, then all the Blue Bayou packages, then the River Belle 1st show packages.
I think River Belle standard brunch probably isn't too bad if you don't have a huge party and are flexible on the time. I personally always just wake up at 6 Am no matter what it is, lol. But like right now there's plenty available for July 22. Even Blue Bayou is available. So I'm guessing it would be ok just to wait until later in the day.
For River Belle Premium or Blue Bayou I would definitely try to book at 6 AM though.