My dd practiced (and still does) about 45min/day, 6 days/wk. She just turned 14 and practices without being reminded about 1/2 the time. At 12, I was reminding her every day. A couple of yrs. ago when she was balking about practice and struggling with hard pieces, I did ease off for a few months and then gradually increased practice time. That seemed to do the trick. HTH.