Supervisors will vary in terms of the amount that they expect you to write, so ask for clarification if you are unsure. Remember the old adage of quality not quantity. If you find yourself writing more material per question than you could get down on paper in an hour, you will be in trouble at the time of exams. In any case, you will likely need to practise writing timed essays closer to exam time.
Finally, if you get stuck, don’t be afraid of asking your supervisors or Director of Studies for advice. We are here to help you and we want you to both enjoy your work and to perform to the best of your ability.