2020 Had Shortest Days on Record

Before this year began, the shortest day since 1973 was July 5, 2005, when the Earth's rotation took 1.0516 milliseconds less than 86,400 seconds.

But in the middle of 2020, the Earth beat that record no less than 28 times. The shortest day of all came on July 19, when the Earth completed its rotation in 1.4602 milliseconds less than 86,400 seconds.

Look up exact daylengths for today or any other date

The speed of the Earth's rotation varies constantly because of the complex motion of its molten core, oceans and atmosphere, plus other effects.

Graph showing true daylengths in 2020

Variation of daylength throughout 2020. The length of day is shown as the difference in milliseconds (ms) between the Earth's rotation and 86,400 seconds.

2021 Is Predicted to Be Even Shorter

Scientists monitoring the Earth's rotational speed expect the trend of having shorter days to follow us into 2021 as well.

According to their calculations, an average day in 2021 will be 0.05 ms shorter than 86,400 seconds. Over the course of the entire year, atomic clocks will have accumulated a lag of about 19 ms. For comparison: in past years, they ran fast by a few hundred milliseconds per year.

In fact, the year 2021 is predicted to be the shortest in decades. The last time that an average day was less than 86,400 seconds across a full year was in 1937

https://www.timeanddate.com/time/earth-faster-rotation.html