Half banana, the first mention of three days and three nights had to do with the story of Innana . She told her companion to wait that long for her to return from visiting her sister god of the underworld. When she didn't because she was killed by her sister the companion went for help.
Innana was the queen of heaven the goddess of fertility and love etc. This story was all about how there's death and no growth during the fall and winter seasons. She was resurrected and others were made to take her place in the underworld during these non productive seasons.