Hey gmatrix -
While there isn't a magic number of hours I can give you I do have some general recommendations to offer. These all stem from information Veritas has collected from instructors and students over the years. Though there isn't one formula for success, these were all strategies employed by people who ultimately saw great success on the exam so I hope they help you!
1) Devote 2-4 months to your GMAT preparation. A two month window might seem surprising but several factors contribute there: if you've got 3-5 hours each day to dedicate to your studies than you may not need 4 full months. Alternatively, if you are just getting started and have some weak areas in quant fundamentals you need to address you'll likely need more than two months to sufficiently address those basics and also master the higher-level questions, test strategy, pacing, etc.
2) Commit to studying 3-5 hours daily. While any practice is beneficial, the GMAT is a long and trying exam. The sooner you begin training your body and mind to sit still and work critically for long periods of time, the better off you'll be come test day. I also recommend naming one day a week your "GMAT free" day to avoid burning out. Do your best to take that one day for yourself and some relaxation without even thinking about the test!
3) Scaffold your approach. Remember, "Practice doesn't make perfect, practice makes permanent." I think it is important to brush up on the basics before diving head first into practice tests and assorted problems. I advise my students to take a practice test at the very beginning of their preparation for two reasons: it provides a benchmark for your progress and it introduces you to the format, timing, and "feel" of the test. From there, use the test's structure to help identify basic areas to cover: arithmetic, algebra, geometry, word problems, probability, sentence correction, etc. My quant was fairly weak when I began studying for the GMAT and I found high school algebra and geometry texts to be incredibly helpful in retraining my mind in the ways of math (many public or college libraries have teacher resource room's full of these textbooks ). Just be careful not to "over -study" from those books. The GMAT is extensive so you want to make sure you don't spend time studying concepts it doesn't test!
4) Make sure you've taken a good amount of practice tests (10-15 is preferable) before you sit down for the official exam. For at least several of them, force yourself to complete the essays as well. You'll be at a serious disadvantage on test day, particularly in terms of stamina, if you've never worked through the two 75-minutes sections after spending an hour crafting two essays.
So at an average 4 hours a day, 6 days a week, you're looking at just shy of 200 hours over two months and upwards of 400 over four months. The GMAT is definitely an investment but if you put it in the time you should certainly see a high return. Best of luck!
