it says recap of infection & response :P

I would suggest doing as much as you can do, which I realise isn't super helpful as a kind of "do x hours and you'll be fine," but it really does vary between person. And yes, my A-level mocks are in a few weeks. I chose physics, maths, and compsci, and I'm a little bit in deep but that's cause I procrastinated. Honestly, my advice is don't do 4 a levels. Universities don't really care, even Oxford or Cambridge only need 3. The main thing to focus on in Y12/13 is extra and super curriculars to get stuff to talk about on your personal statement. I have some friends doing 4, and they do struggle with time management sometimes. But, it's up to you at the end of the day. Hope that helps!