You can complete the CDS syllabus within 60 days if you have in-depth knowledge of Maths, English, and General Science. Each subject has its own importance. If you are talking about completing each subject from the scratch, then it is very difficult. You need to understand the exam and what all topics are asked. You need to learn shortcuts in Maths. You need to learn vocabs, grammar rules, synonyms and antonyms, one-word substitution, etc. GS covers topics such as history, geography, science, polity, economics, current affairs, etc.