You should talk to admissions departments or an admission consultant to be sure, but generally speaking the number of times you take the GMAT is irrelevant. I would advise that you work to hit your maximum score in 4-5 tries. I agree with the previous poster that before walking into the testing center to take the exams you should have achieved your target score a few times on practice exams (in fact, you should probably outscore your target by 20 points on practice exams). Don't hesitate to push back the date of your exam (I think it's a $50 charge to move the date if you are still a week out) if you aren't ready to hit your target...
KW