Hi JyotiChauhan,
Studying for the GMAT now - far in advance of when you will actually "need" your Score - is a smart choice. The amount of additional study time that you might need will depend on your Score Goal and how you are performing on your practice CATs/mocks. Before I can offer you the specific advice that you’re looking for, it would help if you could provide a bit more information on how you've been studying and your goals:
1) How many hours do you typically study each week?
2) What study materials have you used so far?
3) On what dates (or approximate dates) did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
4) What is your overall goal score?
5) Are you planning to apply to any other Schools besides ISB?
GMAT assassins aren't born, they're made,
Rich