I'm not sure if anyone's actually worked it out but I'd be ready to bet that
1. those who did it in (near) minimum hours did it over a short period of time;
2. those who took lots of hours did it over many years
The anecdotes above seem to bear this out. In my case I was category 1 and did it in 48 hours - 1 hour of which was a trial flight in April, the rest done over 3 and a half weeks in August of the same year. I don't think it made me a particularly good pilot, but two or three flights a day definitely means you build up the skill set quickly. (I learned to drive in a week, too - it suits me...)
On the other hand I have a friend who is 67 and likely to take another couple of years - due to breaks for health reasons, &c.
Tim