Hi faheem7791,
Many GMATers spend 3 months (or more) of consistent study time before they hit their 'peak' scores, so beginning your studies now (for a planned Test Date in September or October) is a smart choice. In addition, an initial CAT Score around a 600 is a strong performance (the average score on the Official GMAT hovers around 550 most years).
From what you describe though, your immediate study plan is 'book heavy'; unfortunately, many Test Takers who study in that way end up getting 'stuck' at a particular score level. There's no harm in starting off your studies in that fashion, but you'll likely end up needing to invest in some additional, non-book resources at some point. I suggest that you actually do 'some Quant and some Verbal' each week though (as opposed to the "all of one, then all of the other" that you're planning). You'll likely find it easier to retain everything overall if you're working on a mix of subjects. You should also plan to take a new FULL-LENGTH CAT (with the Essay and IR sections) in about 2 weeks and report back with your score. We can then discuss the results and any adjustments that you might make to your studies going forward.
Before I can offer you any additional advice, it would help if you could provide a bit more information on your timeline and your goals:
1) What “brands” of CATs/mocks do you currently have access to?
2) What is your overall goal score?
3) 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
760+: What GMAT Assassins Do to Score at the Highest Levels