So-called 'leap seconds' are added now and then to clocks around the world because the Earth's rotation actually takes a little longer than the 86,400 seconds that theoretically make up a day.
When scientists began measuring seconds using atomic clocks, they based the value of the second on the speed of the Earth's rotation in around 1820.
But since then, the time Earth takes to turn completely on its axis has actually increased very slightly.
“The atomic second is too short,” explains Andreas Bauch from the time laboratory at the Federal Physics-Technology Institute (PTB) in Braunschweig.
That means that Bauch and his team will slip an extra second into the official time sent to clocks via radio, telephone and internet at exactly 2am.
For a moment, the time will hop from 01:59:59 to 01:59:60 – before proceeding on to 02:00:00 as normal.
Bauch cautions readers against watching out for the unusual time display – it won't actually pop up on the screen of your clock, phone or computer.
“Don't sit there in front of it, it's not worth it. You'll only be disappointed,” he said.
Most clocks will only check in with the radio signal or internet time server a few hours later and update themselves with the altered time.
But for some companies, knowing exactly what time it is will be of critical importance – for example, telecoms companies or those operating high-voltage power grids.
The scientists will be crossing their fingers that all goes well this time around, as despite thorough preparations for the last leap second in 2012, a number of websites including the Qantas airlines booking system were taken offline by the change.