Low GMAT Score, Applying Round 2 - test re-take timing?

[PinkLady]

Hi! I am planning to apply Round 2 to Ross, Duke and Indiana Kelley and hope to focus on CPG brand marketing. My background is in advertising, and I have strong ties to CPG already, so I feel that my career path and goals are relatively strong. I also have some unique work experiences, strong community involvement (board positions for 5+ years), a 3.5 undergrad GPA, and overall have worked hard at building a compelling application. The one weakness in my application is my GMAT, which is well below target.

I have taken a ManhattanGMAT course (twice), and have taken the test (3) times now over the course of the last 2.5 years (I know, I know, that's probably my downfall right there...but life happens, you get busy, blah blah blah). The highest score I've achieved on test day is a 480 (31V, 25Q) and that was in April 2012 right after my second prep class; my highest practice test has been a 530. I re-took the test a week ago and scored a 390 (!!) and I'm feeling pretty hopeless, as that was supposed to be my last try before apps were due. I know I'm smarter than this, just can't figure out why I can't master this test.

I'm having a hard time pinpointing my weaknesses, I know my timing is OFF, I'm either way ahead or way behind and in general the math just seems hard for me, for some reason. I'm making a combination of stupid little math errors at the end of a problem, but am also just flat out missing the approach on many problems. So my next step is hire a tutor to help me focus on a few key areas (since I know can't do them all) and try to eek out as much improvement as possible. Realistically, I am hoping to get into the 550-620 range.

So my question is this: I know that even with a tutor, I'm going to need to put a significant amount of time into this. Initially I was thinking of a dedicated 4 weeks of study, taking 4 day work weeks, and trying to submit a new score to the Adcoms by 1/31, in an effort to reach them while they are still reviewing applications. I know that for Ross and Duke, first round decisions and interview invitations start going out around mid to late January, or even early February. They have both confirmed they will accept a new score post-Round 2 deadline. But, if I were to allow myself 8 weeks of study (end of Feb/early March), I might get better results. How long can I take to study, and still submit a new score to the schools for consideration in this round? I am prepared for the fact that I may get waitlisted and asked to re-take the test anyways, but I do not want to get pushed to Round 3 consideration if I can avoid it.

Any advice is appreciated, thank you so much for your time. However, please don't simply tell me to wait until next year as I have made the decision that this is my year and I am moving forward with my applications. I know I'm well below the 80% range at my schools, and I am facing an uphill battle. I am seeking advice on how to mitigate and move forward with what I have to work with.