Dear Johney,

It varies from student to student and their grasping ability. 

Some take 2 years, 1 year, 6 months, 3 months or a month to prepare for NCHMCET JEE.

You can take as much as time to prepare for your exam.

In order to prepare for your exam you should make a proper plan so that you can easily complete your course and you get proper time for revision. 

You need to practice regularly for your exam especially for mathematics.

Keep your general knowledge up to date. Work on your english.

It is recommended to solve previous year papers and mock test series for your practice. 

Good luck!!