All together in times past (2,3,4)

I believe the answer is:

at one time

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'all together' is the definition.
(thesaurus)

'times past' is the wordplay.
'times' becomes 'at' (I can't explain this - if you can you should give a lot more credence to this answer).
'past' becomes 'one-time' (similar in meaning).
'at'+'onetime'='AT ONE TIME'

'in' is the link.

Can you help me to learn more?

(Other definitions for at one time that I've seen before include "in the past" , "Formerly" , "Taking place simultaneously" , "in former days" , "together" .)

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

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