Insect that's metamorphosed one minute since (5)

I believe the answer is:

imago

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'insect' is the definition.
(imago is a kind of insect)

'one minute since' is the wordplay.
'one' becomes 'i' (Roman numeral).
'minute' becomes 'm' (abbreviation).
'since' becomes 'ago' (I've seen this in another clue).
'i'+'m'+'ago'='IMAGO'

'that's metamorphosed' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for imago that I've seen before include "Sexually mature adult insect" , "Insect at end of life" , "For example, monarch ultimately" , "Comma perhaps" , "Picture of saint" .)

I've seen this clue in The Times.

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