'Days' in the Bible

And the Lord appointed a great fish to swallow Jonah, and Jonah was in the stomach of the fish three days and three nights.

So Jonah arose and went to Nineveh according to the word of the Lord. Now Nineveh was an exceedingly great city, a three days’ walk.

Then Jonah began to go through the city one day’s walk; and he cried out and said, “Yet forty days and Nineveh will be overthrown.”