It is an interesting study. It puts a grounding on success, you really need to concentrate on something if you want to excel. That is why intermediate guitarists shouldn't be disheartened when they hit a roadblock. They have already come so very far and if they concentrate like they have been for years on guitar, then the success will come.
I couldn't tell you how many hours I have done, I just know its not nearly enough. After playing for a year I did start writing it all down on a big chart, trying to reach the elusive ten thousand hours in a year or two (... EXTREMELY HARD). I recommend using a practice log, but don't get caught up in counting the hours, minutes and seconds of your day.
I saw a comedian last night...30 seconds after his show ended he was out front near the merch stand signing autographs. I was one of the first out the door and he was already there for his fans. He did about 90 minutes on stage and would have been very drained, but he knows that time is valuable and he can get alot from it.
If you don't mind reading, look up a book called 'outliers' by Malcolm Gladwell. He uses a number of examples: the beatles, bill gates, apple etc...it is revealed that they all worked ALOT. Talent is overrated.