The head of the department lets them leave one hour before the end of the work day
Question

                I am employee in one of the government departments. The hours of work are 7 a.m. to 3 p.m., but our boss in this department lets us start work at 7 a.m. and work until 2 p.m.. What is the ruling on that part of the salary that is for the hour that I do not work? Is it permissible for me to consume it or should I give it in charity?.
Praise be to Allah.
      If you have no work to be done in that hour and the boss 
      lets you leave, there is no blame on you. But the boss has to fear Allah 
      and strive to do what is in the best interests of the work, so as to 
      fulfil the trust that has been given to him. 

    Shaykh Ibn Baaz (may Allah have mercy on him) was asked about 
    an employee who, when he has finished the work he has, leaves before the 
    workday is over, especially in Ramadan. Is that permissible? 

    He replied: It is not permissible and what he has to do is to 
    stay at work until the workday ends, unless he has permission from his boss, 
    because new work may come along and he may be needed for it. So the employee 
    has to stay at work until the workday is over, unless he has permission from 
    the state or from his boss. 

    End quote from Fataawa Noor ‘ala al-Darb. 

    But if the work requires you to be present during this hour, 
    you do not have the right to leave, even if the boss gives you permission. 

    Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked 
    about a man who asked permission from his direct superior to leave work, and 
    he gave him permission. What is the ruling on his salary? 

    He replied: If you ask him for permission and you know that 
    the work requires you to be present, then you should not accept the 
    permission from him and you have to be present even if you were given 
    permission to leave. But if the work does not need you and you are given 
    permission by the owner of the business, then I hope that there is nothing 
    wrong with that. 

    End quote from Liqa’ al-Baab al-Maftooh, 14/question 
    no. 17 

    And Allah knows best.