The answer to this question really varies widely between teachers. Some teachers insist on 10 or more hours a week. This, in my opinion is unrealistic for most parents from our culture to achieve. If you did practice that much naturally, I think it would be great, but only after a period of preparation on how to practice and what to practice. Otherwise you risk burnout, physical pain issues, and worst of all falling out of love with an amazing activity that everyone can enjoy.
So here are my ideas for how much to practice and how to achieve longer levels of practice. For any new student, practicing 5 times 10-15 minutes + your weekly lesson is a good routine for 3-4 months. For the advancing newer student(4-10 months), 30 minutes is ideal 5 times a week. For the student who has been practicing well for a year, I recommend two one hour practices per week + 3 half hour sessions. This could be pushed then to 5 hours a week over that year. After about 2 years of practicing in this studio, you will have learned how not to hurt yourself, and you will have learned the proper approach to working through material. For someone playing for their enjoyment(as a hobby), we want to totally eliminate the feeling of frustration when learning music. You should not be motivated by a sense of eliminating errors, but by the desire to find something beautiful in what you are playing at any given time and reflecting that quality internally. This will create a profound connection between you, the composer and your audience. It should be a pleasurable experience to play the masterworks of the great composers.
