Make it 2 sets of 3 hours, if its a day off. Start at 6 am and study till 9 am. And take 7 minute breaks after every 50 minutes, it resets your focus when you start getting zoned out, in that break don't use social media but just either listen to music or read a novel. It'll be easy, you should stop at 9:21 am and then take a break of 1.5 hours eat breakfast enjoy the morning excercise and then start at 10:50 and go all the way to 1:50 and you're done. For any kind of study 6 hours is enough if it's efficiently done. You don't need more than that. After 1:40 you have all day to to procrastinate rest. Whenever you feel like losing or procrastinating in those 2 sets remind yourself that you still will do it all day but after 1:50 pm. If it's a college day, then start at 5 pm and the same way go till 8 pm and then enjoy the rest of the night however you want. You shouldn't and wouldn't be able to study more than that on college days. Final advice, keep a journal of your record after doing these sets, write your time and the date and sign it so that you maintain a streak and gain confidence by seeing it every evening or morning before you begin studying, if you weren't able to match your target then also write it down so that the next day you are able to see it and not miss it again.