Admission to IIT after 12th for Undergraduate courses isbased on Jee Advanced scores for Engineering stdeams.

Students must have minimum 75 %aggregate marks in 12th from recognised University or Must be in top20 percentile of respective board in General category for eligibility  To engineering streams. 

IIT and NIT are national importance University as per Government of India for Btech/MTech/Msc/B. Arch/M. Arch courses.

These colleges need atleast 75%aggregate marks in 12th for eligibility 

Exams ljke Jeemain is accepted for NIT and Jee Advanced for IIT.

All details below. 

https://engineering.careers360.com/articles/join-careers360-campaign-for-joint-counselling-for-over-50000-seats-in-iits-nits-iiits-cfti

Daily 3hours of study is minimum because 8hours of sleep and 6hours of coaching and 6hours of college is norm. 

You are left just woth 4hours every day for study out of whi h 1hour should be given to relax and stay fit. 

On weekends you must devote 7hours atleast. 

There is no common counselling for CEED 2019 to be conducted by IIT Bombay. The participating institutes will hold the CEED 2019 counselling individually for admissions to M.Des. Candidates will have to apply separately for admissions to these institutes. Individual institutes are likely to conduct an aptitude test or interview

First of all, let's talk about 12th Marks 

Anything more than 75% will work.

Now for IIT, the First step is to qualify JEE Main, which you will qualify if You score more than 90 marks out of 360 in JEE Main, considering any variation.

Now In JEE Advance if

Navnret books are good and kucid but lack indepth coverage and has lower level problems  

For MHTCET ww recommended books by Marvel Publications which is best. 

For Jee Main We recommend NCERTbooks  

For Jee Advanced you need to also study from reference books like OP Tandon for Chemistry , HC