Hey, I revised just over a month before my GCSE's and improved on all my subjects since mocks (9A*2A) and its not impossible, although I have quite good memory which I think may have helped. I split the my time focusing on one week per subject. Doing a different subject everyday just gets confusing. All I used for my science GCSEs were the CGP revision guides and memorised each one whilst crossing off the content on the specification. Writing notes would've been a waste of time with very little time left. Then at the end of the week if you have time , do practice questions. GCSE content seems like a lot at first because of all the extra stuff you go through in class but once you've gone through the whole content at thoroughly at least once, you can easily go through it in a day and repeat the notes off by heart. Subjects like maths I tried to do half an hour a day again learning the theory from the revision guides or watching youtube videos (hegarty maths was good and concise) but more on doing past papers. Make sure when you do A-levels that you start being organised though, because this method definitely did not work for my AS-levels and I regret it now. It's hard trying to be on top of things when you're so used to doing something last minute. Also, waking up at around 4am on the day of exams helped a lot to cram last minute information (but that may not work for everyone) Good luck.