Hello Aspirant

Writing CAT in the final year itself, saves a one year because if the results are as per your expectations, you will get your desired college as soon as you are out of your graduation. On the other hand, if you prepare for CAT once you have graduated, you are certain to lose one year and also will have additional pressure of finding job.

I would suggest you should join the right offline or online coaching and kick start your preparation at the earliest. Best wishes for CAT:)