Twelve going up or down (4)
I believe the answer is:
noon
'twelve' is the definition.
(twelve noon)
'going up or down' is the wordplay.
I cannot quite see how this works, but
'going' could be 'on' (both can mean functioning or activated) and 'on' is located in the answer.
The remaining letters 'no' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for noon that I've seen before include "See 8" , "[LUNCHTIME] ?" , "Twelve o'clock in the day" , "12 o'clock" , "High time of day?" .)