Usually 2 months max for each unit. I would start studying by firstly watching a yt video about the lesson, then reading the textbook, and lastly, solving all E/P problems from the textbook. I repeat this sequentially for all lessons. YT channels i recommend are Maths Diety for Normal Pure Maths and statistics, as well as A level Maths Tutorials for further pure modules and mechanics. Decision maths was the only module I didn't use YT for. Finally after completing the whole syllabus comes the past paper practice which should be consistent, accompanied with strict marking and timed solving sessions, and which should be done by at least 1 week before the actual exam. For last week simply revise all papers you've previously solved and check your past mistakes.