Negative answer to "Will you be off at twelve?" (4)
I believe the answer is:
'twelve?' is the definition.
(I've seen this before)
'negative answer to will you be off at' is the wordplay.
I cannot really see how this works, but
'negative' could be 'no' (no is a kind of negative) and 'no' is located in the answer.
'at' could be 'on' (location) and 'on' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for noon that I've seen before include "[LUNCHTIME] ?", "See 8", "when PM starts", "12 pm", "High time of day?".)