Crossword Genius

When a notion can seem heartless (4)

Ross

I believe the answer is:

noon

I'm a little stuck... Click here to teach me more about this clue!

'a notion can seem heartless' is the definition.
I can't judge whether this definition defines the answer.

'when' is the wordplay.
I cannot quite see how this works, but
'when' could be 'on' (I've seen this in other clues) and 'on' is present 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 "12 o'clock" , "High time of day?" , "when PM starts" , "Twelve o'clock in the day" , "A moment of time" .)

I've seen this clue in the Evening Standard.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.