'Three day' in the Bible

So Jonah got up and went to Nineveh according to the Lord’s command.Now Nineveh was an extremely large city, a three-day walk.

Now Nineveh was a very large city, requiring a three-day journey to cross through it. As Jonah started into the city on the first day's journey, he proclaimed the message, "40 days more and Nineveh will be overthrown!"