Is the rotation of the earth getting slower?
Due to the tides the rotation of the Earth is getting slower. The Moon atracts the water, which acts as a brake on Earth's rotation.
Other effects can be the wind, the movement of magma in the Earth's mantle, and the melting of glaciars, but these effects, while smaller are imprevisible.
Many of millions ago, the day could be 23 hours long, and many million years from now, can be 25 hours long.
At the human scale this effect is very small. We may say that during the 19th century the day was exactly 24 hours, since the "medium day" (actually the second) was defined by those times.
By now it is about 24h and 2 milliseconds. These milliseconds add to a whole second every two or three years, and for compensating this, leap seconds are added to set the clocks with Earth's rotation.