Are the extra hours that are calculated for the salary permissible, knowing that no work is done during them and one simply waits for his father's meeting with the factory owners to end?

The questioner and the worker are considered special employees who deserve wages by surrendering themselves for work, whether they actually worked or not. If their remaining in the factory after official working hours was with the consent of its owners and their work was considered overtime, then they are entitled to wages for the extra hours, even if they only waited for the factory to close during that time.