source: How long is a day?⌚ | How long is a day?⌚ | By StarTalk | Facebook
A regular day that we are familiar to is a Solar day, but it is not a full rotation of the Earth. There is a thing called Sidereal day.
And even The length of a solar day is not actually 24 hours, it is just 24 hours on average.
Also, Earth rotation can’t be used for time keeping, because it’s unstable that way.
Turns out, The Earth is slowing down. So a day is becoming longer.
There are many Things that change the rotation of the Earth. But all factor combines, Earth day has been increasing.