It varies from person to person. Some candidates take 2 years to prepare for the exam, while some students only need 6 months to crack the papers with the highest marks. It depends on how much time you need to complete all the subjects in the course, the syllabus, and how soon you can put the knowledge into action. The best way to score the best marks is to start at least a year before the exam date and get really strong on all your fundamentals.