Up until 150 years ago, each New Zealand region had its own, different time zone. …
In 1866, the first cable across Cook Strait was laid and regions between Napier and Bluff became connected by telegraph. Variations in operating hours at the relaying and receiving offices along the line initially hinder the smooth transmission of messages. So, in 1868 the Telegraph Department proclaimed that all offices had to adopt Wellington time.
This move lead to a parliamentary decree establishing a single time for the whole country – the first implementation of standard time in the world, which came into effect on November 2, 1868.
Source: 150th Anniversary of NZ Standard Time | Measurement Standards Laboratory.