Supporter of union supplied with rota, saving time (10)

I believe the answer is:

federalist

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'supporter of union' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?

'supplied with rota saving time' is the wordplay.
'supplied with' becomes 'fed' (feeding is a kind of supplying. I am not sure about the 'with' bit.).
'rota' becomes 'list'.
'saving' is an insertion indicator.
'time' becomes 'era' (an era is a period of time).
'fed'+'list'='fedlist'
'fedlist' going around 'era' is 'FEDERALIST'.

Can you help me to learn more?

(Another definition for federalist that I've seen is " One sort of politician".)

I've seen this clue in The Times.

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