Downright discontented setter's punching worker's lights out (7)
I believe the answer is:
bedtime
'lights out' is the definition.
(I've seen this before)
'downright discontented setter's punching worker's' is the wordplay.
'discontented' says to hollow out the word (remove centre letters) (the word's contents are removed).
'setter's' becomes 'im' (I am - referring to the crossword setter).
'punching' is an insertion indicator (inserted letters punch or puncture others).
'worker' becomes 'bee' (a worker bee).
'downright' with its centre taken out is 'dt'.
'dt'+'im'='dtim'
'dtim' inserted inside 'bee' is 'BEDTIME'.
(Other definitions for bedtime that I've seen before include "Hour to retire" , "Lights out" , "When to turn in" , "eleven o'clock?" , "when story comes out?" .)