Hi Fastener,
Based on your plan and score goal, there are some things that you should keep in mind.
1) A 620 is a relatively modest goal, but it's still close to the 70th percentile overall - which means that most Test Takers do not score that high on the Official GMAT.
2) Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores, so limiting yourself to just 2 months of study might keep you from your score goal.
Since it sounds like you're just beginning your studies, then it would be a good idea to take a FULL-LENGTH practice CAT Test; you can download 2 for free from
www.mba.com (and they come with some additional practice materials). That score will give us a good sense of your natural strengths and weaknesses and will help provide a basis for comparison as you continue to study. A FULL CAT takes about 4 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.
1) When are you planning to apply to Business School?
2) Going forward, how many hours do you think you can consistently study each week?
GMAT assassins aren't born, they're made,
Rich