The Tenancy Tribunal was established by the Residential Tenancies Act 1986. Some procedural matters are governed by that Act, and others governed by the Residential Tenancies Rules 2010. You can find copies of Acts and Rules at legislation.govt.nz.
Timeframes for any court or tribunal are subject to all sorts of factors and no estimate can be given with any real certainty. One thing to keep in mind is that, when a Tenancy Tribunal application is filed, you will first be offered a free mediation service before matters progress any further. You may therefore be able to resolve the difficulty at an early stage and without having to proceed to a hearing. You may receive a decision at the end of the hearing if the matter progresses that far and is simple and straightforward. Otherwise the ‘Tenancy Adjudicator’, who is the person who would be making the decision, would write up his or her decision and send it out as soon as possible.
Delayed decisions are called ‘reserved decisions’. These are appropriate where the Tenancy Adjudicator needs to give careful consideration to evidence or points of law raised at a hearing rather than make a decision then and there. Reserved decisions can take some time to come out. By way of general guidance, parties to a civil dispute in the District Court can usually expect a reserved decision to come out within 3 months of the last hearing day for the case.