It was when Creon announces what the oracle has told him.
Oedipus, the lord of Thebes, has sent Creon who is his brother in law, to the Apollo to request that the oracle on advice on how end the plague. Creon returns, bearing news: once the one who murdered the past ruler, Laius, is discovered, Thebes will be restored of the torment and the events after that begin.
The inciting incident is a scene, plot point or occasion that guides the audience into the story. This specific minute is the point at which an occasion pushes the hero into the principle activity of the story.