Fiction: Write a flashback from present day where your character relives a core memory and reflects on their growth (ex. a bad date, your goth phase, etc.)
Poetry: Pick a unit of time and personify it as a whole or its intervals (ex. what would meeting a year feel like? Or what if November met February?)
Non-fiction: Share a moment of time standing still or something you wish could stretch into infinity.

If there's a book that you want to read, but it hasn't been written yet, then you must write it.