It is very very close to consistent, but days are very slowly getting longer. Thanks to tidal interactions, the moon steals a little of Earth's angular momentum every year and gets a little further away. That makes the day a tiny bit longer and the tilt of the orbit a tiny bit bigger. At the start of the Triassic 252 million years ago, there were about 400 days per year, and the moon was about 6000 miles closer.