On the low end, the gyms in my area tend to do 3 days for 3 hours. I rarely see them do more than 12 hours ( 3x4, or 4x3 ). However, I do see some girls come in for extra conditioning or open gym or partake in the tramp and tumbling programs to get more hours in.
In summer, I've never heard of 5's doing 15, though I suppose they could if the parents, child, and coaches saw to it.