How do IIT JEE students manage to study 14 hours a day?
Do not take too much load. Do not force yourself too much, do that much your brain can digest. IIT JEE is considered one of the toughest exams. Yes, to get a good score and admission to IIT you need to study a lot but do not do that beyond your capacity. With preparation you need proper diet and should sleep well, at least 6-7 hours per day. You will not able to study 14 hours a day constantly, even if you manage to do that for one day, from the next day your productivity will decrease. You can not hold it. At the time of preparation quality will matter rather than quantity. You need a proper planning that will be effective for you. I would suggest you to connect with IIT JEE mentors. They can guide you in a proper way during your preparation.