Scientists will hold back time this weekend, making Sunday one second longer than any other day this year.
A "leap second" will be inserted by scientists all over the world into the atomic time scale at midnight, June 30 UTC (Co-ordinated Universal Time), corresponding to noon, July 1 in New Zealand.
UTC is the primary time standard by which the world regulates clocks and time.
When the leap second is added, New Zealand's atomic clocks will display '11.59.59', followed by '11.59.60' and '12.00.00', and Radio New Zealand listeners will hear an extra time 'pip' before the midday news bulletin.
The brief halting of the second hand will prevent our atomic clocks speeding ahead of solar time based clocks, compensating for the gradual and unpredictable slowing down of Earth.
The planet takes just over 86,400 seconds for a full 360-degree revolution, but "the rotation of the Earth is gradually slowing down, due to the drag of tides and other effects, and the duration of a day is getting longer," MSL director Tim Armstrong said.
The concept of leap seconds was introduced in 1972 to ensure that the atomic time scale never differed from the rotation of the Earth by more than one second.
At the introduction of leap seconds, the atomic time scale was set to the length of one day.
"Without leap seconds, eventually our clock time would get out of step with the time of day we expect from the location of the sun in the sky," Dr Armstrong said.
"If they were not introduced then eventually the solar midday would occur at midnight."
The decision to add a leap second is made on an irregular basis by the International Earth Rotation Service, which collects data from observatories around the world to determine the length of the day, Dr Armstrong said.
Since 2000, there has been discussion about abandoning leap seconds, which are considered a nuisance for people wanting to maintain continuous time scales, he said.
A meeting was held in January of this year to decide the fate of leap seconds but was an agreement could not be made. A meeting in 2015 will reconsider the matter.