Part-time eventually? (4,3)

I believe the answer is:

some day

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'eventually?' is the definition.
Both the answer and definition are adverbs. Perhaps there's an association between them I don't understand?

'part-time' is the wordplay.
'part' becomes 'some' (I've seen this before).
'time' becomes 'day' (day is a kind of time).
'some'+'day'='SOME DAY'

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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