Hello Aspirant,
See there is no any hard and fast rule to study for particular hours because it depends upon the capability of an aspirant. 

See there are total 23 IITs in India which itself are the most prestigious engineering institutions of India but among them also there are some best IITs such as IIT Madras, IIT Bombay, IIT Kharagpur and so on. Now to get into such IITs for B.Tech course you need to have good rank around in top 2000 in JEE-Advance and to be eligible to appear in JEE-Advance you should clear the JEE-Main at least with the qualifying cut-off of JEE-Main of that year. 
To secure such rank in JEE-Advance one should follow the right and smart track of preparation because only hard work will not work in the huge competition of today's life. So I am enlisting down some smart preparation tips which will help you in your preparation of JEE-Advance so that you can get into the best IITs of India :-

>>>>>> Very first thing is go through the syllabus of JEE-Advance and categorize it as easy, average and difficult.   https://engineering.careers360.com/articles/jee-advanced-syllabus

>>>>>> Make a proper time-table to balance your studies and daily routine work  and give little more time to studies.
>>>>>> Go for the best study material which can make you more confident while solving the question of JEE-Advance because it will boost your moral. 
>>>>>> Don't forget to make notes while studying because it will help you in memorizing the important things in the last time prior to exam.
>>>>>> Practice previous year's question papers and sample papers along with different mock tests as many as you can because it will enhance your self-confidence and time management skill.   https://engineering.careers360.com/articles/jee-advanced-question-papers
& 
https://engineering.careers360.com/articles/jee-advanced-mock-test

>>>>>> Don't forget to do exercise and yoga regularly to keep your body mentally and physically fit.

You can check out the link given below for best preparation tips :-
https://engineering.careers360.com/articles/jee-advanced-preparation-tips-physics-chemistry-and-mathematics

I hope this information helps you.
Good Luck!!