It is a common notion that IIT JEE is tough. As a matter of fact any other competitive exam is as tough or as easy as IIT JEE.
It is just that the IIT JEE Paper would require a different approach. With the right guidance and sustained preparation IIT JEE would not be tough.
There is no end to IIT JEE Preparation. So there is no question of how much study one should do. Prepare as much as you can, and you can crack it.
Wish you all the best.
Ashwin (IIT Madras).