Yes! It may seem like a waste of time, but allowing yourself to stop, breathe, and think can make your essay so much more concise, and thus likely to score higher. If you rush into your essay, too concerned about time limit, then you are more likely to miss easy points and, even worse, your introduction will be haphazard at best. Most markers will say they have an idea of what score they will give an exam paper by the end of the introduction, so it is absolutely worth taking five minutes to ensure that your introduction is a coherent summary of what you will be saying. As for the rest of your essay, you should not be worrying about the quantity you can achieve in the time provided, but the quality. As long as you sum up a few points in a cohesive, intelligent way, you will tick the boxes and impress enough to get those higher marks. The easiest way to come up with those cohesive, intelligent points? Planning!