Dear applicant, mostly instructions like this to study for around 2hrs to prepare for boards is very common. This is often said based on the weightage or importance of JEE Mains. If you invest more time of yours to prepare for broad questions asked in the boards and miss the Multiple choice type then that would hamper your JEE preparation. So all the MCQs of Physics Chemistry and Mathematics have to be solved to crack JEE Mains.

Good luck!!!