Currently, the opening hours of a Public Service or a Channel are specified using a Period Of Time entity. The opening hours relation does belong on this entity, since it does not make sense that a period of time defines opening hours.
I believe the opening hours were added after this issue, where there was a need to specify opening hours in a certain period. For this, the schema.org OpeningHoursSpecification seem like a better fit. Note that this is still a topic of discussion on schema.org aswell.