Well…anytime! You can take the test at any point you think you are ready. There are certain myths that the GMAC s/w keeps on getting easy and difficult around the calendar…even if there is any truth attached to it, you can do nothing about it. Hence, give no heed and take the test when you think that you are at the peak of your preparation.
There are two approaches…
Gain sufficient experience and when you see that you have gained enough professional maturity, plan your MBA and take GMAT at least one year before commencement of the course. This is a good strategy when you intend to have substantial work-experience before starting your MBA.
Take the GMAT in your final year of undergrad or soon after you finish your college. This is a good strategy when you wish to start your MBA with just 2-3 years of experience. This would create a good back-up plan for you and you can plan your career ahead.
Although the score is technically valid for 5 years, please be advised to apply with a score not more than three years old.