Crossword Genius

At a precise moment when hand is fully raised? (2,3,4)

Ross

I believe the answer is:

on the hour

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

'at a precise moment' is the definition.
(exactly on the hour)

'when hand is fully raised?' is the wordplay.
I cannot really understand how this works, but
'when' could be 'on' (I've seen this in other clues) and 'on' is found in the answer.
'hand' could be 'hour' (hour hand is a kind of hand) and 'hour' is present in the answer.
The remaining letters 'the' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for on the hour that I've seen before include "When the minute hand is vertical" , "at sixty-minute intervals?" .)

I've seen this clue in The Times.
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