Is seniority based with time in the respective company. But require a certain amount of total time, at least 1000 hours Part 121 time with the respective link operator and have completed at least two Operational Competency Assessments after your check to line, with a pass mark acceptable to the Training Manager, passed a command development course and associated coursework and interview.
Of course this is all variable depending on what requirements Air New Zealand would also like turboprop captains to hold, as the requirements seem to change every six months when word from on high is sent down.