The first study I know of is the 1996 book "The Road to Excellence" http://www.amazon.com/Road-Excellence-Acquisition-Performanc... . I got it after I read Peter Norvig's essay on "Teach Yourself Programming in 10 Years." http://norvig.com/21-days.html .

So here are the numbers, in short, for mastery:

It takes about 10k hours of practice.

It takes about 10 years.

That means about 3 hours of practice everyday. Everyday.