Hi Jagdishkumar,
Your GMAT Score is 'valid' for 5 years, so the length of time between when you take the GMAT and when you apply to Business School will likely NOT be a factor in how that Score is interpreted. If you Score a 700, then that shows Business Schools that you are a really strong critical thinker overall (and while GMAT Test Taking skills can fade over time, those broader critical thinking skills generally do not) - so a high GMAT Score that is several years 'old' is still a valid indicator of how well you will probably handle the MBA Program(s) that you choose to apply to.
From your post, it's not clear whether you are just beginning your studies or you have put in some significant study time already. Either way, taking the GMAT far in advance of when you'll "need" your Score is a smart choice.
If you're just beginning, then it would be a good idea to take a FULL-LENGTH practice CAT Test; you can access 2 for free from
www.mba.com (and they come with some additional practice materials). If you want to do a bit of practice first, so that you can familiarize yourself with the general content and question types first, then that's fine - but you shouldn't wait too long to take that initial CAT. A FULL CAT takes about 3.5 hours to complete, so make sure that you've set aside enough time to take it in one sitting. Once you have those scores, you should report back here and we can come up with a study plan.
I'd like to know a bit more about your timeline and goals:
1) What is your goal score?
2) When are you planning to take the GMAT?
3) When are you planning to apply to Business School?
GMAT assassins aren't born, they're made,
Rich