What I've learned from surfing the web in a couple of weeks, started off with the
MGMAT books, talked to fiends and alumnus, etc. is that GMAT is very much doable! The concepts that GMAT uses both in the quant part and the verbal section are fairly easy. Your job is to recognize the problems and know what method to use to solve the question. How long that will take for you depends on your background, abilities, etc. etc.
I've had friends scoring over 700 with less than a month practice, while other have studied for 3 months and scored below 700.
It all depends on your preferences. But have in mind that almost everyone can get a really high score on GMAT if they just put in the time and effort!
My recommendation is to look at the forums guide to build a study plan and then start as soon as possible! When you have started to study you will get a feeling how hard it is, and what you have to study extra.
One idea could be to early take a practice test, to early see your strengths and weaknesses and focus your study, since you don't have so much time!
Only you can decide what is the right method for you!
Look at my first post, to see my study plan!
Cheers!