Book edited - back issue reveals when to retire (7)
I believe the answer is:
bedtime
'when to retire' is the definition.
(I've seen this before)
'book edited back issue' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'edited' becomes 'ed' (publishing abbreviation).
'back' says the letters should be written in reverse.
'issue' becomes 'emit' (both can mean to give out or radiate).
'emit' in reverse letter order is 'time'.
'b'+'ed'+'time'='BEDTIME'
'reveals' acts as a link.
(Other definitions for bedtime that I've seen before include "when story comes out?" , "when one's due for retirement?" , "The hour for retiring" , "Lights out" , "When to turn in" .)