If I take engineering then how much time should I give per day to studies?

First year is quite easy. Afterwards, study duration depends on the branch like for CE, 2nd year is damn easy whereas 3rd year requires handwork.

It's not about how much time you are devoting to studies. It is all about being efficient and smart studies. Focus on lectures, be good in your note making. Revision of what was taught in class will be enough for days. However, practice the numerical subjects on regular basis.