20 hours?
I have heard 1000 repetitions to make a reflex and 10,000 hours to mastery. I have not heard 20 hours before.
20 hours of me drawing hands and they are probably not at the point of having the correct number of fingers yet.
Heya. You're right, it does take 10 k hours to master something (from Outliers book). It's equivalent to drawing only hands for 5 years on a full time job. It's pinpointed at people aiming to be at the top of their field so my reasoning is that doing so will put you on the same level as the old masters (hand wise at least).
To learn a new skill and be "good" at it, it seems that you need 20 hours of focused learning (Roughly 45 minutes every night during a single month).
Source:
He talks about the 10,000 hours at around the 3 minute mark. ^_^