Thanks for the A2A.
When one is giving exam on D-day, there is no MCQ that asks you to choose how many hours you studied in a day or how much sleep you sacrificed.
There are however questions on the paper that you can answer if you are well prepared on the subject matter.
For that one requires atleast 3 revisions of all the 19 subjects and practicing as many swts and gts as possible. In how much time you can pull off the above, dictates how much time you should put in daily. It varies from individual to individual. Some may grasp fast but forget a lot while some may take time but possess long term memory.