One of my friends studied at IMS Kolkata so I am aware of it. At that time he was doing a job and simultaneously doing a course at IMS. However, he did not perform well in DI/LR with the pressure of his job. And get a call from CAP, IIMs, MDI, IIT Delhi, FMS, IIT Madra, VG SOM, IMT G.
Here is the review of IMS Kolkata -
Therefore, you can join IMS as it is good. Apart from it, you must also take test series and Time Study materials to practice so that you can perform well.