Many Yoga schools today practice a session that runs for 60 to 90 minutes. If you are available to do it every day, it would be fantastic. However, if your schedule would not permit it, and you can only go to class once or twice a week, you can do sessions at home. Any practice of Yoga is better than not practicing Yoga at all. Spending your time 20 to 30 minutes every day is much better than spending your 90 minutes in a session once a week.