Hi there,
I suppose someone could get lucky on the GMAT by guessing correctly. However, given that there are 37 Quant questions and 41 Verbal questions, and given that each question gets harder as you get questions right, I think you'd have Vegas-like odds for winning big with little studying.
If you have little time to prepare, it is even more essential that you "study smart." I recommend checking out various materials and programs, and deciding which best fits your learning style. Learn all the methodologies and tricks, chug through problems and read the solution key to fully understand the correct way to solve ones you missed, and take a few practice tests.
I was actually pleasantly surprised with my score. I studied for 10 hours a week for two months, with one book and CD, and I got a 750. I hadn't taken a practice test for a few weeks, and I assumed my score would still be somewhere in the high 600s. In my case, I just needed to polish the rust off of my skills (worked at Microsoft for 5 years, and hadn't seen a standardized test in as many) and then they came out as strong as before. My case is atypical, though, as I got a 1500 on the SAT and worked as an SAT tutor through college. For someone who is learning these standardized test skills for the first time, or who requires significant improvement, I don't think such "luck" would be possible in such a short amount of time.
Everybody is unique, and each person has to create a study plan that will work for himself. However, to be quite honest, I think that some of the study plans that people present on this site run the risk of being overkill. Too many different strategies can confuse you, and studying for most of the day for a series of weeks can burn you out.
This is just my humble opinion. Best wishes,
Tatiana
Tatiana Becker | GMAT Instructor | Veritas Prep