hi! i wish i had the mindset in year 11 that you have. i realised how fked i am too too late and now i am sad.
well done. what i'm going to say is only what works for me, but i think it is really effective and you can try it if it seems reasonable to you.
I believe the easiest way to divide time amongst my subjects and studying effectively for them is by creating a study timetable.
I would recommend you to study as much as you can (with breaks ofc), but also make sure you get at least 7 hours of sleep.
However, around 3 weeks before exam block, you should have a study timetable that you would stick to for those weeks, and study intensely.
For the holidays, you should wake up early (9-10ish) so you don't feel bad for sleeping in, have food etc, but then get straight to work! You should also have a study timetable for these two weeks.
I'm not too sure of how to explain how to make a study timetable ... you just do. If you want to see mine, I am more than willing to pm it to you, just chuck me a message!