I have not seen any recommendations from USAG for JO/DP. I can say that gyms seem to be in certain ranges on hours. Coaches also have their thoughts on # of hours. Ours seem to feel that too many hours, especially under age 13 can lead to injuries later on and burnout. Our levels seem to do well, win top 3 team placements at just about every meet so they have no reason to push more hours....
But that is for non-elite path. Most gyms around here with girls on elite path will require homeschooling and more hours.