The Earth’s rotation has been on a gradual slowdown since its birth.
The day lengthens every 100 years by about .0015 seconds. It’s not much, mind you, but in several billion years it all adds up.
At that time, for instance, a month will have increased from 27.3 days to 47. But don’t worry: we won’t be around to experience it anyway, the expanding sun will have gotten us by then.
In 2010, a massive earthquake in Chile shifted the earth’s crust so much that it changed the speed of the earth’s rotation. The difference in speed was so small that we didn’t notice it.