Coruscant would have gone through a gradual transformation from an all-natural world to an ecumenopolis.
When was it an almost 100% natural world, without civilized settlements? (Meaning the only settlements were villages and the kind of stuff you can't see from space.)
When did large cities visible from space start forming?
When did serious urbanization start happening, and how long did it take until 100% of the planet was a city?
I'm OK with EU canon.
Related: What did Coruscant's nature look like before it was urbanized?