It depends on your age and natural talent for the game of course...
But if i had to guess, for the average person... I'd say ~8 hours a day 5-6 days a week, >10 tournaments a year, a coach wouldn't hurt, a passion for the game would be a must.
Actually I'd have to revise that. For the average person this may not be possible at all really. 2 and a half years wouldn't normally be enough time. Of course it's not impossible, just unlikely.
I'm a 1450-1500 player and I was wondering what it would take to reach the title of national master in about 2 and a half year?