A Mere 50 Years

As an elf Frieren lives for thousands of years and thus has a warped perception of time, with her casually inviting her normal friends to watch a once-in-50-years event, without realizing they would the end of their lives by them. When she reunites with her friend Himmel 50 years later for the event, she's shocked to see he's now an old man.

Example of:
Time Dissonance