Does it really matter? That for being a top student an individual have to study for continuous hours?
I personally think that hours don’t matter because the thing which matters is how much focus you are on the entire time you are studying. Well if you are finding difficulty in focusing and stretching your study hours then you need to plan a bit.
Listing down the things which you should instantly add to your daily diet to enhance focus and study time:
Caffeine

A great quality espresso, green tea, and not to miss a dull chocolate are a great wellspring of caffeine. With ground-breaking cancer prevention agent properties, regular stimulants, caffeine can encourage focus and enhance your concentration towards your study time.
Blueberries

A measure of blueberries day by day can fundamentally enhance the working of the mind and shield the cerebrum from oxidative pressure.
Nuts and Seeds

Great wellspring of vitamin E and fundamental greasy oils, for example, omega-3 and omega-6. Cashews, almonds, walnuts, peanuts, flaxseed, or even nutty spread are solid fats fundamental to the psyche and body.
Entire grains, Beans, Pomegranate Juice, Avocado additionally bolsters the working of a sound cerebrum.
So now as you asked how many hours of study are healthy for a top student. So it usually depends on the kind of the preparation you are doing. Well, 8 hours a day is considered healthy for a student to study throughout a day.
"All The Best"