According to MBIE, the answer to that is six months, and they don't feel any need to inform the requester of the expected timeframe.
Back in August 2017, after Thompson and Clark Investigations had been caught spying on Greenpeace for Statoil, I made a number of requests to government agencies seeking information about their relationship with New Zealand's most infamous private spy agency. One of those agencies was MBIE. In September, they coughed up an invoice, but extended answering the request for communications because it required searching through a large volume of information. A couple of weeks later, they said this:
The Ministry has decided to grant your request; however the response is still subject to final approval. I apologise for the delay in getting the information to you, and will endeavour to send it without due delay.
No response arrived. Eventually, when TCIL was caught spying for another government department, I noticed the non-response, and queried it. At which stage they eventually responded. I wasn't happy with how long the response had taken, so asked for information about their communications around the handling of the request. Their response last week attempted to explain the delay by saying that it had been combined with similar requests from other parties (who we know from past media reports to include Greenpeace and Oil Free Wellington). Consultations on this apparently hadn't ended until January, and they only bothered assembling the response they had promised in September once those responses had been sent. Whether this counts as "without undue delay" is left as an exercise for the reader.
MBIE's behaviour here, in promising a response and then not delivering it for six months, is simply deceitful. And the lesson for requesters is that if an agency tries this stunt, you should demand a concrete and close date for the response, remind them when it approaches, and go immediately to the Ombudsman if they fail to keep their promises. Otherwise, you're effectively letting them grant themselves an unlawful indefinite extension, which undermines the entire purpose of the Act.