How I revise is a bit confusing but I'll try to explain it.
For bio, definitely go through the course specification. Learn all the wordings you need for marks. I did this for highers like a week before the final exam and it was STRESSFUL so try to do that early on.
Physics and chem do practice questions online/from a textbook. Don't do past papers too early you want to save the questions for closer to the exam. Also see if there's any exact wordings you need to learn
Do really early past papers (idk your exam board but I have past papers from 1990-2002) and see if you have access to any past prelims - you want to save the actual exams from more recent for before your actual exam. If this is the actual exam you are asking about, then around 2 weeks before the exam start with later exam papers (2010 onwards).
Don't overwork yourself though or you will burn out <3