When he's around one moves quickly (4)

I believe the answer is:

hies

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

'moves quickly' is the definition.
(I've seen this in another clue)

'when he's around one' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'he's' could be 'hes' and 'hes' is found in the leftover letters.
No letters remain.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

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