Whether time is sufficient largely depends on how quickly you work. Q and V sections give you 75 minutes each to solve 37 and 41 questions, respectively. That means an average of 2.02 min/q for math and 1.83 min/q for verbal.
Obviously, some questions are more difficult than others. A good general rule is to never spend more than 4 minutes or so on a single question (unless it is near the end of the test and you have plenty of time left). If you do not get it or come very close by then, you probably won't get it. It is better to make an educated guess and move on with the rest of the test.
The GMAT penalizes you for not finishing, so definitely aim to finish each section, even if it means just guessing at the end.
The best way to get a feel for the timing is to take some practice tests and see how you do. I would recommend starting with a test from the GMATPrep software to simulate real conditions and see where you stand. That also tells you your weaker areas and what to concentrate on next.