Hi,
Its ambitious but achievable. Its besides the point how much time you study, its how you study. Try to understand what you do and really understand it. Of course, time is important because you don't want to over exhaust youself but if its that much important to you, as you say, go for it.
I first test I took, I scored 450. That was in February. Since then I have been studying, not on a very regular basis I might add, and I am hitting at 620 these days. Maths was my problem. I hired personal tutor, got offical GMAT prep material and studies when ever I had time, not preocupying myself too much.
Also, don't forget, GMAT is only one of the components B-schools consider. My school's avarage is 690 and I was told by my admissions advisor that 620 will be fine due to other parts of my application which, according to admission board, are very strong. So you see, perhaps you will be fine with little less then 700.
Good luck