Hi Laya,

You don't need so much time to worry about CAT exam preparation for MBA at IIMs. Since MBA syllabus comprises of Quantitative aptitude, logical reasoning and Data Interpretation, and verbal ability, a thorough preparation of 6-8 months is sufficient. However, since there will be some hiccups in your preparation because of internal exams, semester exams, college fests etc. so to prepare well and be on safe side, you can start your preparation from B.tech. 3rd year and be thorough and well prepared for your CAT exam by your final year of B.Tech.

Good Luck