The absolute minimum is 30 minutes a day.
Just as with bi-weekly lessons, if you have only 30 minutes every other day or 10 minutes daily, your progress will be so slow you will question whether you are wasting your money and both yours and your teacher's time.
If you don't have 30 minutes every day, wait until you do. Even then, you should get in some extra time on weekends or whenever your time off is.
You might be interested in how often to have a lesson.
copyright 2002, Martha Beth Lewis, Ph.D.
Contact me for reprint permission.