How long should I spend on each corse over a week? Should I do it daily?

I am thinking of using Khan Academy but I don't know how long I need to spend on it each week. Some other websites with curriculums say 60 mins 3x a week. some even say 30 mins 3x a week. Some say 20 mins daily. I don't know how long I should spend each week on each course. I am homeschooled and interested in using khan academy. Does it differ per class? Please help. Thanks, Myles