Seriously? Think about your question for a moment. You can't possibly get a definitive answer, and even if you did it would be meaningless. Are you going to base any decisions on something like 'at Durham I can study for 6 hours but Oxford needs 8'? There are so many variables (natural ability, reading speed, clubs and society memberships, social life etc). Generally speaking (big disclaimer) the workload for a particular course will be similar at similarly-ranked institutions.