Night owl? Write a story about a morning person.
Morning person? Step into the head of a night owl.
Afternoon your time of day? If you like early afternoon, write about late night. If you like the time closer to evening (sunset), write about early morning (dawn).
Step out of yourself and try to sincerely imagine what it is like to be someone else who lives differently from you.
If you think that morning people are all obnoxious and too happy, try to figure out why you think that way and what it feels like to them. If you think late-nighters are just slobs who like to avoid work, do the same thing.
Open your mind to other people’s lifestyles and figure out why it works for them. That doesn’t mean you have to approve of it or appreciate it. Just understand it. If it’s not your thing, then that’s okay. But try to figure out why that is. Try to understand yourself and the rest of the world with this exercise. If you get stuck, ask someone you know who is on a different sleep schedule from you.