try to take note of when you might be feeling sick of it and be sure to take some breaks! it might be remotely doable for some people but studying that many hours a day is really taxing. You can probably improve efficiency in some areas and study less for your sanity
I did 3u maths last year and I studied for a full week before the HSC & trials. Looking back on it, I was studying really inefficiently (doing questions that weren't sufficiently challenging) and I ended up procrastinating a lot during my studies because I was so sick of it. I could've probably completed the amount of study I did in 3 days of full focus & assessing questions to make sure they're useful for me to attempt.