Ohio School Lunch Time Regulations?

I attend Black River High School in Sullivan Ohio. The school gives us 30 minutes for lunch. I have lunch 7th period. But my 6th period history teacher takes time off our lunch. For instance, if someone talks when he says not to, he makes us wait an extra minute after the bell to leave for lunch. He has shortened our lunch period by up to 5 minutes on some days. Can he do this? Does the state of Ohio require a certain amount of time for school lunch?