'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!”

But God prepared a worm when the morning rose the next day, and it smote the gourd that it withered.

The Lord said, "You were upset about this little plant, something for which you have not worked nor did you do anything to make it grow. It grew up overnight and died the next day.