Hang on a second - when will it be high noon?

The extra second is added to compensate for the gradually slowing rotation of the earth. Photo / Thinkstock

There is never enough time in the day but tomorrow, at least, there will be one extra second.

A so-called leap second will be inserted into the atomic time scale at midnight on June 30, universal time - which is midday today, New Zealand standard time.

A leap second-enabled clock will progress through 11:59:58, 11:59:59, 11:59:60 and 12:00:00.

The extra second is added to compensate for the gradually slowing rotation of the earth.

Measurement Standards Laboratory of New Zealand (MSL) said without leap seconds, the solar midday would eventually occur at midnight.

It is the 35th leap second since its introduction in 1972.

MSL said without leap seconds there was no clear strategy to prevent atomic time and the perceived time of day from getting out of alignment.