Against time taken, unless initially undetermined (5)

I believe the answer is:

vague

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'initially undetermined' is the definition.
'vague' can be an answer for 'undetermined' (thesaurus). I'm not sure about the 'initially' bit.

'against time taken unless' is the wordplay.
'against' becomes 'v' (abbreviation for 'versus').
'time' becomes 'age' (an age is a period of time).
'taken' indicates putting letters inside.
'unless' becomes 'u' (this might be a standard abbreviation which I don't know about).
'age' enclosing 'u' is 'ague'.
'v'+'ague'='VAGUE'

Can you help me to learn more?

(Other definitions for vague that I've seen before include "Hazy" , "Indistinct or imprecise" , "Indefinite" , "Uncertain, imprecise" , "Obscure, undefined" .)

I've seen this clue in the Sydney Morning Herald.

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