Dude, I only study 2 hours a day, and in between 20-30min
rest.
Its not about how long, but how much u absorb inside. I have
friends who can study an entire chapter for 2-3 hours a day, and at
the end, they don't understand what's being said. Then I have some
who only study 1 hour and he can remember quite a lot.
Its not about who's smart or stupid, who needs longer or shorter
time 2 study, but its about what u study and whether u can absorb
inside. If u feel that u have learn enough for the day, take a
breather, and then try 2 write down the things that u have learnt
about the chapter/lesson. Go through them again the next day before
u start on a new chapter. Hope it helps.