Working hours of teachers as per indian law

I am working in a school managed by an autonomous organization under ministry of HRD. Our day starts from 7.30 am to 1.30pm six days a week. Three days a week, we have to attend the school from 3pm to 4.30p. Monthly once our work starts at 6am and ends at 10pm without any mention of break as per the official orders issued by our head quarters. What are the laws that guide the working conditions and hours of teachers. where should we approach for grievance redress.