Answer: At sunset
In the movie Shrek, the princess turns into an ogre at sunset. This transformation is a key plot point in the movie, as it reveals that the princess has been cursed with a spell that turns her into an ogre every night. This curse is eventually broken when she falls in love with Shrek, who accepts her for who she is, regardless of her appearance. The transformation at sunset adds a sense of urgency to the story, as the characters must race against time to break the curse before it becomes permanent. Overall, the transformation of the princess into an ogre serves as a powerful metaphor for the importance of accepting others for who they are, regardless of their outward appearance.