If a teacher is covering for a class at school, does he work overtime? Because what else would he have done during that time?

Teachers are not paid hours. They are committed to such hours of representation. They are counted, however, just as unusual hours are counted, e.g. if a class is on a class trip, or if there is another destiny.

Ideally, he would have freed, would prepare lessons, document iwas, write/read e-mails, clean up/organize something or he would have ‘free time’ where he goes home, eat something, or stay with a coffee with colleagues.