Today's last minute is destined to be 61 seconds long, for timekeepers are to add a "leap second" to compensate for the wibbly-wobbly movements of our world.
The ever-so-brief halting of the second hand will compensate for a creeping divergence from solar time, meaning the period required for Earth to complete a day, the Daily Telegraph reported.
The planet takes just over 86,400 seconds for a 360-degree revolution. But it wobbles on its axis and is affected by the gravitational pull of the Sun and Moon and the ocean tides, all of which brake the rotation by a tiny sliver of a second.
As a result, Earth gets out of step with International Atomic Time (TAI), which uses the pulsation of atoms to measure time to an accuracy of several billionths of a second.
To avoid solar time and TAI moving too far apart, the widely used indicator of Coordinated Universal Time (UTC) is adjusted every so often to give us the odd 86,401-second day.
The adjustments began in 1972. Before then, time was measured exclusively by the position of the Sun or stars in relation to Earth, expressed in Greenwich Mean Time (GMT) or its successor UT1.
This will be the 25th intervention to add a "leap second" to UTC.
The extra second is added to UTC, also known as Zulu time, only ever at midnight, either on a December 31 or a June 30.
Time-catching is as irregular as the Earth's rotation itself. The last three adjustments were in 2008, 2005 and 1998. The year 1972 saw two additions, followed the next seven years by a second every year.
The vast majority of the world's seven billion people are likely to be blithely indifferent to tomorrow's change, except for a few who may note the curious fact that they will live a second longer.
Every time a second is added, the world's computers need to be manually adjusted, a costly practice that also boosts the risk of error.
High-precision systems such as satellites and some data networks will have to factor in the leap second or risk provoking a calculation catastrophe.
For this reason, rocket launches are never scheduled for leap-second dates.
