Who keeps time on the internet? It’s probably something you haven’t much considered before. But every internet-connected device, of which there are billions, has an onboard clock, and not all of them are synced up to keep time precisely.
In everyday life, the focus of timekeeping tends to be on minutes rather than seconds, but an inaccuracy of a single second on the internet can cause issues such as missed reminders, or in serious cases, the delay of a spacecraft launch. Leap seconds, one-second adjustments occasionally applied to Coordinated Universal Time to accommodate the difference…
Source CNET Tech