A few points about applying for an MBA which I would have liked to have known when I was in my final year..
1) A very poor GMAT score (less than 600) can keep you out on its own but even a good GMAT score (720+) cannot take you in on its own.
2) Most top US Schools do not have a 2 year minimum work experience cut off. It is more about what you have done than how long you have worked. There are people who have got in with less than 2 years. That being said the average years work experience at matriculation is 4-5 years. So average work experience while applying would be 3-4 years.
3) IMO, it is better to do away with the GMAT as soon as possible, giving you enough time to do your b-school research and write your essays during application season. Opinions may vary from person to person.
4) B-school research is much easier when you have a clear idea about your short term goals.
All the best..