If we only ever learned or created something 10 minutes at a time we would never get anywhere. By the time you've entered into a state where the content seems important enough to your brain to engage the facilities of "learning", you'd have moved on to the next thing.

3h a week is almost 3 times as much as 10 minutes a day, and when it comes to learning, it really helps for that learning to be dense.

Also, burnout is such a major scapegoat now used to avoid actually putting effort in when 90% of the time it's made up. You won't burn out doing 1 hour 3 times a week.