Hello dear aspirant
B.Tech classes in Kerala normally starts in July. The rest depends on the college,  each college has a different process and it entirely depends on the college,  when to start the classes. But it starts nearly in July.

Hope I am clear

Hello Roshan, 

For most of the colleges in india the classes for the students can start anywhere between 1 week of july to 2 week of july. You will be notified by your respective college about its opening.

I hope you will find my answer helpful. 

All the best.