Always remember " it’s not about how much hours we study a day , it’s all about How efficiently do it ". There may be several reasons or purposes which may affect your studying capacity.
One should have a strong reason / purpose / passion to study for long duration. Whenever you sit for studying remember your aim, and be ready to work hard for it.
One should set a study environment around you. Always sit on a table and study.
Study continuously for 55 minutes and take 10 minute rest.
Remove all the possible distractions around that divert your attention from studies.
Always try to study at least 2 subjects a day as it breaks the monotony of the studying process.
Keep a chilled water glass near you, drink a sip or two whenever you attention diverts.
You may give 6-7 hours for study a day on weekend. Also, try to maintain notes for whatever you study as this will help saving your time in revision.
You may also refer to the earlier notes made by some experts on the subject which you are going to study , as this may give you a hint about what you will study and help saving a lot of time in understanding the concept.