What any doe may become, eventually

I think it could be either:

Which length description are you looking for?:

3,3

oneday

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'eventually' is the definition.
(I've seen this before)

'what any doe may' is the wordplay.
'any doe' can be anagrammed to 'ONE-DAY'.
Though, I'm unsure how the anagram is indicated.

'become' acts as a link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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