You wont need more books.
The amount of time you need, no one can tell you.
It depends on where you are now, where you want to go, and what score you would settle for vs what you would aim for.
On average, I would say that most
people who score in the 700's seem to take anywhere from 150-200 hours of study to do it BUT.....
That being said.... I know people who score 780 without studying. I know one guy who studied on a TRAIN RIDE to the thing and got a 720. I know others who studied for months on end and couldn't break 600. I went from 600 to 730, but it took me from Feb to June, 4 months, with at least 20-25 hours a week. All told, I'm confident I put in over 350 hours, and may very well have put in over 400. Counting practice exams, add 72 more hours to my total. There's a post somewhere where I actually caculated it. My study partner put in even more than me, probably 30 hours a week average - pushing 500 hours of study - he went from 600 to 680. For some lucky few, the GMAT is a "one week hassle". For others, it's a "two month pain", for others, its a "five month long ulcer" and for some, it takes a year. I have one friend for whom it took two years to get to 640 from the mid 400's.
In short, you may find that you are 50 points away from your target score. You may find that you are 100. Or maybe 200 points away. You may be 50 hours away from your score, you maybe 5. You may be 500 hours away.
Study for 2-3 days, just to "sharpen" the mind and take a practice exam from Kaplan
or Princeton or someone else (dont do GMATPrep yets). Evaluate yourself. How far are you from your goal? Do you have a goal?
As you begin this journey (and it is a journey) remember that the GMAT is a marathon, not a sprint.
Post your study plan here, people can critique.
Number one mistake people make:
1. Look at problem
3. Try to solve
4. Get it right
5. Move on to next problem as if somehow they magically now understand the problem because they got it right.
Number two mistake people make:
1. Look at problem
2. No idea how to do it
3. Try anyway
4. Give up and look how they solved it
5. Say "Oh I see... ok"
6. Move on
Looking at their solutions for a minute wont teach you what you dont get. Don't make this mistake either.