Hi Srinivas Kumar,
To answer your immediate question: the 16-day wait period between Official GMAT attempts ONLY applies to Tests taken in the same 'format' (re: Test Center Date to Test Center Date OR Online Date to Online Date). Scheduling your Exam in one format does NOT impact when you can schedule an appointment in the other. That having been said, 'rushing in' to retest might not be a good idea - especially if you significantly under-performed on this first attempt. There might be broader issues that are impacting your performance - and 5 days of additional study might not be enough time to fix them all.
Before I can offer you any additional advice for your studies, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) Have you received your Scores yet for your 1st attempt? How did you Score (including the Quant and Verbal Scaled Scores)?
2) How long have you studied? How many hours do you typically study each week?
3) What study materials have you used so far?
4) 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)?
Goals:
5) What is your overall goal score?
6) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich