Below is some helpful information about students are the restrictions on hours worked.

When employing any school-aged students, their work hours must be outside of school hours only and not between 10pm and 6am including in times that interfere with the student doing school work. 

It is unlawful for businesses to employ school-aged students during school hours under Section 30 of the Education Act, unless they have a certificate of exemption.Failure to do so can lead to fines up to $1,000 for both the parents and the employers.

Education Act 1989 – New Zealand Legislation

https://www.employment.govt.nz/starting-employment/rights-and-responsibilities/young-employees/