Long time shut up in seraglio (3)

I believe the answer is:

era

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

'shut up in seraglio' is the wordplay.
'shut up in' says the answer is hidden in the clue.
'ERA' can be found hidden inside 'seraglio'.

(Other definitions for era that I've seen before include "8" , "Specific time" , "Long historic period" , "Geological age" , "Distinctive period of time" .)

I've seen this clue in The Times.

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