hi,

see CAT exam is basically have questions from quantitative aptitude, reasoning, verbal and logical reasoning, english, data interpretation etc. if you go through the analysis of cat previous years papers you may realize that questions are not very much difficult but you have to be very fast while answering the questions. refer to the below link to know about cat syllabus:

https://bschool.careers360.com/articles/cat-syllabus

however at the time of 4th semester to 5th semester students prepare for campus interviews, so you also need to revise the aptitude questions for campus placement. so its time to start your preparation right now. students of final year of graduation are also eligible to appear in cat, make a daily routine and devote atleast 3 hrs for preparation. at the 4th year you may buy the mock series and give test at home.

hope it would help.