You can definitely do it in 8 weeks if you're determined.
I recommend getting
Manhattan GMAT set of 8 books, they're very useful for mastering concepts, plus of course the official guide from GMAC.
With 7 to 8 hours a day, you can finish the
MGMAT books in the first 3 weeks, then the official guide in about 2 weeks. After 5 weeks, you'll be able to identify your weakness and problem areas.
In the final 3 weeks, spend as much time as you can attacking your weaknesses, and then end your studying plan with some practice tests, the set of 8 books from
MGMAT has 6 free practice tests, and GMAC (the creator of GMAT) offers 2 free prep tests on their website, which are pretty useful in estimating your actual score on the test day.
Best of luck.