Eight hours, but not on the night shift (7,3)
I believe the answer is:
working day
'eight hours but not' is the definition.
I can't tell whether this definition defines the answer.
'on the night shift' is the wordplay.
I cannot quite understand how this works, but
'on' could be 'working' and 'working' is found in the answer.
'shift' could be 'day' (day shift is a kind of shift) and 'day' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for working day that I've seen is " See 6".)