Hi sakgupt,
As long as your GMAT score is "valid" (meaning that it is not more than 5 years old), then you will be fine. Business Schools do not care how "old" your score is (again, as long as the score is from some time within the prior 5 years to when you apply).
Many Test Takers spend 3 months (or more) of consistent study time during their preparation for the GMAT. During that time, it's common to spend 10-15 hours per week (or more) on the process. You might need more or less time overall, but this general information should help you to plan ahead and figure out when you can reasonably study for (and take) the GMAT.
GMAT assassins aren't born, they're made,
Rich