In 5th Grade she basically covered a page each week of the book.
I think if you do it though you have to adjust your goals from a typical JH Beginning Band Class. Kids are much smaller in 5th grade and it takes a little bit of adjustment there. I would aim for the goal of good solid tone and note reading primarily. If you could get half to three quarters of the way through the beginning band book by the end of the year you're doing good. The key for their program was to follow it up the next year with review and build on those fundamentals.
Good luck if you end up doing it! There aren't a lot of 5th Grade Band Programs remaining!