IMO its not a matter of a set number or years, but more a question of whether they can achieve a number of outcomes in their cricket set up:
- produce some quality pace bowling that will be able to bowl test sides out
-improve the fielding dramatically, especially the out cricket ( the catching seems to be coming alog nicely at the moment though)
-produce some batsmen with the technique to succeed in all conditions- this means good defence and development of cross bat shots
-remove the petty politcing/ intrinsic corruption among the administration
-better development of the abundant youth talent
- prepare pitches that allow for balanced cricket
this one is the crucial one and if this is achieved from grass roots level all the way to the top, the other outcomes will fall into place- ie more kids will want to become pace bowlers if they see the pitches accomodate this skill, the batsmen will learn to play a more complete game etc.
Whether india will ever get to the top in the near future is questionable, however. On one hand they certainly have the potential due to population factors, but on the other hand the problems in their cricket set up are deep seated and will be difficult to overcome- so for the mean time id say india would struggle to reach the top and stay there for any length of time- the set-up is just too flawed. Look at the team now, for instance, and they have somewhat of a golden era of talent, especially in the batting, yet despite of this are still a fair way from CONSISTENTLY being a top side.