Legal questions about labor and overtime

Questioner

my son is 15 and works in a supermarket. They are scheduled for blocks of 2 hours. They have been assigned a specific aisle that they have to fill and they use a 'filling colli' method for how many colli have to be filled per hour. If they do not achieve this, they will have to continue working, but only in their own time. So it happens regularly that he only comes home 1 hour or 1.5 hours later. My question is, is it correct that the employer is allowed to do this or does he have to pay for the hours worked? For example, in the collective labour agreement for supermarkets VGL, article 10.1.a states that overtime is considered to have been worked if, after consultation between the employer and the employee, the employee has been instructed to work longer than the normal working hours, and that this will be paid. I would like to know if the time they work is 'own time' or if it is paid time. Suppose it is own time, then he can go home if he is not finished yet?

Lawyer

Depending on the agreement, he may be entitled to payment. That is because he works. I have successfully approached employers before.