You're right that my numbers are off. I'd bee thinking of the end of the Late Heavy Bombardment 3.8e9 years go, but there's some suggestive evidence there was liquid was on Earth's surface 4.4e9 years ago. And the earliest bacterial fossils are from 3.5e9 years ago, though goodnesss knows how long it took bacteria to make colonies that ended up making fossils to survive to the present day.