Isca study time

It is more than sufficient but It will be very large at the time of revision before exam day.

Can anyone quantify it no. of hours it takes for a normal average student

I think if u study from VALECHHA book it will require approx 35 days @ 3 hrs per day i.e 4 pages per day except chapter 3 CONTROLS.

It  is difficult to gain confidence in the subject if you refer study material only. It is better to get some good reference books and save your time. Better option go for manish valechha (not dinesh madan). valechha is well presented with proper explaination, diagrams and memory codes.