The hours you must pay a worker the National Minimum Wage or National Living Wage for depend on the type of work they do. This does not depend on the worker's occupation - it depends on the basis you pay them on. For minimum wage purposes there are four different types of work: time work, salaried hours work, output work and unmeasured work.
This guide describes how for minimum wage purposes you should calculate the hours worked by workers doing output work.
'Piece work' or 'commission work' may sometimes be output work for minimum wage purposes.