In a newsagency recently I saw a note from the owner to an employee saying stay longer if you think you need to. This is like a customer saying to a retailer sell me more products if you think I should buy them. You are a retailer, you will want to sell as much as possible. An employee will want as many hours as possible, especially if, as in this case, the hours are overtime.
My management advice today: do not let employees set their own hours. Be the boss, be responsible for the operating costs of the business.