Coaching generally takes place in various batches once all exams are over.

There are various time slots available and batches in phases have been rolled out for repeated students.
All fee details have been shared below along with refund details and course duration with commencing dates.


https://www.allen.ac.in/2017-18/iit-jee-main-advanced-coaching/courses-for-jee-main-advanced-2017-18.asp

Hello,
As far as i know coaching generally starts after the month of April/May i.e after completion of all engineering entrance exams and ALLEN INSTITUTE is best known for preparation of jee mains and advanced.
You can visit their official website to get to know full details about this.
Good luck.