There is no scientific evidence or consensus that Earth's day length has stalled at 19 hours for a billion years. The length of Earth's day, or the time it takes for the Earth to complete one full rotation on its axis, has varied throughout geological history due to a phenomenon called tidal acceleration.
Tidal acceleration is caused by the gravitational interactions between the Earth, the Moon, and the Sun. Over long periods of time, these interactions can cause changes in the Earth's rotation. Currently, the length of a day on Earth is approximately 24 hours, but it has not remained constant over geological time.
In the distant past, when the Earth was forming and still undergoing various processes, the length of a day was much shorter. As the Earth gradually cooled and solidified, tidal interactions with the Moon caused the planet's rotation to slow down. This process led to an increase in the length of Earth's day over millions of years.
However, it's important to note that the exact duration of Earth's day in the past is not precisely known for periods extending billions of years. Estimating the length of the day during ancient geological eras is a complex task that involves studying geological records, ancient sediment layers, and astronomical data.
While the length of Earth's day has changed over time, there is no evidence to suggest that it has been consistently stalled at precisely 19 hours for a billion years. Such a claim would require extensive scientific evidence and research, which is currently not available to support this specific scenario.