The Motor Vehicle Disputes Tribunal was established by the Motor Vehicle Sales Act 2003, and its procedures governed by Schedule 1 of that Act. You can find copies of Acts at legislation.govt.nz.
Timeframes for Motor Vehicle Disputes Tribunal cases
Timeframes for any court or tribunal are subject to all sorts of factors and no estimate can be given with any real certainty. However, in an attempt to give a very rough and general estimate, you may expect to have your case resolved or otherwise determined within 3 months of an application form being filed.