Hi mp123,
To start, a 600 is a strong initial CAT Score (the average score on the Official GMAT hovers around 540-550 most years). That having been said, raising a 600 to a 720+ will likely take at least 2-3 months of consistent, guided study - and you'll have to make significant improvements to how you handle BOTH the Quant and Verbal sections. Unfortunately, with your current timeline, you have less than 6 weeks of potential study time. As such, you will likely need to change your score goal or change your timeline/application plans. Before I can offer you the specific advice that you’re looking for, it would help if you could provide a bit more information on your goals:
1) When are you planning to apply to Business School?
2) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich