MBA Entrance Exam

Various coaching classes are
1. T.I.M.E
2. IMS
3. Catking

Hi,
For getting admission in IIMs your graduation score should be 60% or above.
CAT score of IIMs closes at 99 percentile itself.
But IIM, Indore and Raipur as tracked in last two academic years take students scoring 96 percentile as well.
It depends on the availability as well.
It is better to target IIM, Lucknow.
Score above 99.4percentile.

Unfortunately, with that score, you cannot get an interview call even from a decent B-school. I would suggest you either opt for a retake (only if you seriously believe that you can score much better than that) or target the other upcoming exams like SNAP, XAT, etc.

Preparation for anything depends on how quickly you learn. There are people who start one year before and some 3 months before the exam date. Personally, for an average student with moderate grasping and commitment towards the test can take 4 to 5 months for proper preparation along with mocks.

As far as CET is concerned a good score will always change depending on the number of students getting the same score. However a score above 100 is good and 130 is excellent as per 2017 trends.
https://www.shiksha.com/mba/ranking/top-mba-colleges-in-nagpur/2-2-0-156-0
Above is the link to best colleges in Nagpur accepting CET scores along with their fees and placement structure.

Your previous academics are definitely good. However, you seat in IIM's depends on your CAT scores and performance in GD/PI.