Just to give you an idea:

I strongly believe that if you digest OG books you will be fine.

OG 11 - 800 questions
OG Review Books : 600 questions

So you have 1400 questions to learn:

1) What is tested
2) Why is an option CORRECT ?
3) Why are the other options WRONG ?
4) What are the common wrong answers ? How does GMAC trick people ?
5) etc..

And this process takes around 8-10 minutes per question. ( Yes even for the ones that you get correct ) So;

1400 questions x 10 minutes / question = 14,000 minutes = 234 hrs

If you study 2 hrs between Monday thru Friday = 10 hrs
Study 6 hrs during the weekend = 12 hrs

22 hrs / week so it will take you roughly around 11 weeks

If you take 6-8 CAT ( 4hrs each ) you can add another week to your schedule and finally I can say:

3 months is an ideal time. ( I rounded all the numbers to the higher ones )

Hope it helps! This calculation is based on so many assumption and the reality will be different for everybody but it can be used as a reference. ( At least IMO )

Good luck!

Kewl! This helps... Thanks a lot!