An excellent question, @RBOpfer!
But the answer is not so straightforward because it is almost like asking:
“How long should a person’s legs be?”
“Well, long enough to reach the ground.”
So, how long you need to study for the GRE depends on a number of factors:
I. What school do you want to go to?
This is one of the first questions to answer. Start a list of schools that you want to apply to and then research what the average GRE score is for the most recent class of accepted students. These average scores give you a target score to work toward.
Also, pay attention to the Verbal and Quantitative scores for students in the particular department and discipline that you will apply to. These scores will be more useful than the average score of students across the entire school.
Schools do not make it easy to find this information, and they may not even publish these statistics. But there are secondary sources that provide this type of information. Also, if you get on the phone and talk to some professors or people in the department you plan on applying to, and ask very nicely, they may provide you with some anecdotal information. I want to emphasize using a phone and not writing an email. Talking on the phone will be straightforward, efficient, and effective. It also puts the person on the spot to provide some kind of answer. And tell them it doesn’t need to be an “official” statistic; tell them your situation and let them know that any information they can provide will be helpful.
II. What is your score right now?
Before you begin studying, you should assess your skills and your level by taking a complete practice test. If you don’t have time for a complete test, some diagnostic tests are available, which are short and approximate your level. Either way, you need to figure out where you are at–what your starting point will be. After learning about the scores of recently accepted students, you may find that you are not too far off the mark. In this case, you may not need to spend too much time studying. But if you find that you are many points away from the average, then you will need to have a much longer and intensive study period.
III. What is your discipline?
Some students forget that they are physicists or literature graduate students. Physicists will need to demonstrate to their prospective schools a strong competence on the quantitative portion of the GRE. Obviously, a strong verbal score will help their chances of being accepted, but the inverse isn’t necessarily true: a weaker verbal score won’t necessarily eliminate an application, as long as the quantitative score is strong. The same goes for a literature major–a weak quantitative score won’t eliminate an application. The admission committee will be looking for a strong writing and verbal score when making a decision.
If you do bomb a section, though, this will not bode well for an application. So, make sure that you are performing competently in both sections. But put an emphasis on the section that most reflects your major and discipline.
IV. So how much time do I have to study?
In my experience as a teacher and a tutor, students can prepare for the GRE in as little as two weeks with intensive study. But these students started with a strong score and didn’t have to relearn any facts or skills. They just needed to learn the test.
On the other end of the spectrum, after a long absence from school, students may need three to six months to prepare for the GRE. In these cases, students need to relearn how to divide fractions, find the prime factors of a number, expand their active vocabulary, and improve their reading comprehension skills. Again it depends on a lot of factors.
V. What now?
Plenty of test prep books exist that you can work through on your own. Classes and tutors can help you with coming up with a study plan if you need support. The software that Barron’s Test Prep provides will actually create a study plan for you based on when you want to take the test and based on an assessment of your skills so you don’t have to think too much about it. You just have to do the studying and practice often.
VI. Other Resources
Article on what to do 24 hours before the test
Article on what to do a week before the test
Article on how to structure your study time