If all of Earth's ice were to melt and flow into the oceans, it would have a significant impact on the planet's rotation. The mass of the ice would cause the oceans to become more massive, and the distribution of this mass would change as it moved from land to sea.
As the mass of the oceans increased, the planet's rotational velocity would slow down slightly. This would cause the length of a day to increase by a few milliseconds. However, the overall impact on the planet's rotation would be small compared to other factors that affect the length of a day, such as the tidal forces of the Moon and the Sun.
The melting of all of Earth's ice would have much more significant impacts on sea level. The melting of the ice caps and glaciers would cause sea levels to rise significantly, which could have a number of consequences, including flooding of coastal areas and the displacement of millions of people. The melting of permafrost in the Arctic would also release large amounts of methane, which is a powerful greenhouse gas that could contribute to further warming.