Hi,

You should finish your JEE syllabus by January first week so that you get at least one month for revising class 11th portions once again. Also, you can do the revision of the class 12th portions simultaneously with your board preparation since the topics will be same.

So 4 to 5 hours study starting form 11th class will be helpful for JEE. As the exam date approaches, say 6 months from the JEE Mains, the study hours need to be increased to 8 hours. Give more focus on revision and solving last year's JEE Mains and Advanced question papers.

Hope this helps

Wish you luck