Erato having to leave for day (3)
I believe the answer is:
era
'for day' is the definition.
(day can mean an era of time)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for era that I've seen before include "Important date" , "Long period of history" , "Significant time" , "Series of years" , "Characteristic period" .)