"Three days" means a span of 72 hours, used to mark deadlines, waits, or travel plans. It usually implies consecutive days in a row, regardless of weekends or holidays.
Fiction was invented the day Jonas arrived home and told his wife that he was three days late because he had been swallowed by a whale. Gabriel García Márquez
Fish and visitors smell in three days. Benjamin Franklin
You Americans, you treat the Third World in the way an Iraqi peasant treats his new bride. Three days of honeymoon, and then it's off to the fields. Saddam Hussein
After three days without reading, talk becomes flavorless. Chinese Proverb
Anyone who goes hungry for three days will be inclined to steal. Korean Proverb
Woman was born three days earlier than the devil. Korean Proverb