New Zealand Daylight Time
New Zealand has two time zones. The main islands use New Zealand Standard Time (NZST), 12 hours in advance of Coordinated Universal Time (UTC) / military M (Mike), while the outlying Chatham Islands use Chatham Standard Time (CHAST), 12 hours 45 minutes in advance of UTC / military M^ (Mike-Three).
During summer months—from the last Sunday in September until the first Sunday in April—daylight saving time is observed and clocks are advanced one hour. New Zealand Daylight Time (NZDT) is 13 hours ahead of UTC, and Chatham Daylight Time (CHADT) 13 hours 45 minutes ahead.
On 2 November 1868, New Zealand officially adopted a standard time to be observed nationally, and was perhaps the first country to do so. It was based on longitude 172° 30′ East of Greenwich, 11 1⁄2 hours ahead of Greenwich Mean Time (GMT). This standard was known as New Zealand Mean Time (NZMT).
In 1941, during the Second World War, clocks were advanced half an hour, making New Zealand 12 hours ahead of GMT. This change was made permanent from 1946 by the Standard Time Act 1945, at which the time at the 180°E meridian was made the basis for New Zealand Time. NZST remained half an hour ahead of NZMT, and the Chatham Islands 45 minutes ahead of NZST.
In the late 1940s the atomic clock was developed and several laboratories began atomic time scales. A new time scale known as Coordinated Universal Time (UTC) was adopted internationally in 1972. This was based on the readings of atomic clocks, updated periodically in accordance with time variations in the Earth's rotation by the addition or deletion of seconds (called leap seconds). The Time Act 1974 defines New Zealand Standard Time as 12 hours in advance of UTC.
In 2011, the New Zealand dependency of Tokelau moved its time zone forward by 24 hours, by skipping 30 December.
Starting in 1909, the Honourable Sir Thomas Kay Sidey annually put forward a bill to advance the clocks an hour from September to the following March and The Summer Time Act 1927 succeeded: first Sunday in November to the first Sunday in March. This proved unpopular so The Summer Time Act 1928 revised this to a half-hour shift from the 14 October 1928 (second Sunday) to 17 March 1929 (third Sunday), then The Summer Time Act 1929 fixed this half-hour shift to run from the second Sunday in October to the third Sunday in March. In 1933, the period was extended from the first Sunday in September to the last Sunday in April. This continued until the Second World War, when emergency regulations in 1941 extended daylight saving to cover the whole year with annual re-applications until the Standard Time Act of 1945 made the abandonment of NZMT permanent in 1946, so that 180° becomes the base longitude and what was called N.Z. Summer Time (NZST) became N.Z. Standard Time.
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