The families of the 29 men killed in the Pike River mine explosions say 15 weeks is not a long enough to carry out a comprehensive Royal Commission.
The commission on Monday issued the first details of the planned hearings, including the parties to be heard and the matters to be investigated.
It has allocated 15 weeks for the hearings in four blocks between May and November.
A spokesperson for the families, Bernie Monk, thinks it will take a lot longer than that to examine all the key issues and he does not want any shortcuts taken.
A preliminary hearing on 5 April will allow involved parties the chance to comment before the details are finalised.
The Engineering, Printing and Manufacturing Union says overall, it is pleased with the details, though president Andrew Little says he would like to be more focus on the Labour Department in its role as an investigator and as a health and safety regulator.