Hm... That's a tough one. If you have lessons, it's a better idea to not have lessons on Sunday; that's the day you need to catch up on school work. Fridays and Saturdays are good for lessons. If you are in the school choir or something, and you also are in the volleyball team (or another club/team), than you should alternate between the two activities if they are at the same time. Most likely they won't be. If you are practising at home, I recomend praticing for 15 to 30 minutes. If you have a lot of free time, than a hour. I hope I helped.