Hi alchya,
Your scheduled appointment time at a Test Center has NO bearing on when you schedule an At-home GMAT appointment. As such, you could schedule them on the same day if you wanted to. That having been said, doing so would NOT be a good idea, nor would scheduling two appointments too close together on the calendar. The process of taking a FULL-LENGTH Test requires a significant amount of energy and effort - and takes time to 'recover' from. This is one of the reasons why you typically shouldn't take more than 1 CAT per week - and your last CAT should be taken about 1 week before Test Day. If you take the GMAT and end up with a Score that you're not happy with, then you need time to recover - and to put in some additional study to hone the necessary skills to earn that higher Score that you're after.
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) How long have you studied? How many hours do you typically study each week?
2) What study materials have you used so far?
3) On what 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:
4) What is your overall goal score?
5) When are you planning to take the GMAT?
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