'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.

Jonah set out on the first day of his walk in the city and proclaimed, “In 40 days Nineveh will be demolished!”

When dawn came the next day, God appointed a worm that attacked the plant, and it withered.