For my HS kids, I don't like practice charts. As others have said, kids will just lie and parents will sign it. I also don't think you can one-size-fits-all say "practice x minutes" for high school. No other teacher says "work on your homework for x minutes every day." They say "here is the assignment, get it done." I do frequent playing tests in class, and recording assignments. I definitely find that many of my students play their recording assignment over and over again until they get it right...sounds a lot like practice to me.