No offence to anyone, but I don't think its the time limit that jeopardises people, but its more tilted towards bad time management. To overcome this, experience is required and knowing how to handle certain situations definately helps. You probably have heard this hundreds of times over your schooling career, but if you can't do a question, don't stew on it and waste valuable time. The point to take away is that if you can manage your time well in ANY exam, time limit should never be a problem.
P.S, knowing how much time you have to do the exam helps as well. =]
EDIT: time allocation should be a delicate balance between accuracy and speed. You don't want to be too pedantic since you'll waste time on minor details, yet you don't want to rush and make careless mistakes. To find the right balance, do practice tests(eg. past HSC's/trials) and see how well you do. Some people can manage to do a 2 hour test in an hour with little mistakes yet some people may take the whole 2 hours to go through the whole test accurately. Alot of textbooks use a mark/time allocation which i think is really stupid. After all, HSC's are designed to get progressively harder, so the earlier questions will be easier than the later ones. Time allocation is different with people, so try to find your balance. =]
