Are you up for a long time? (3)

I believe the answer is:

era

I'm a little stuck... Click here to teach me more about this clue!

'long time?' is the definition.
(a long period of time)

'are you up' is the wordplay.
'are' can be anagrammed to 'ERA'.
But, I am not sure how this is indicated.

'for a' acts as a link.

Can you help me to learn more?

(Other definitions for era that I've seen before include "Long period of time" , "Important date" , "Long historic period" , "Special time" , "Period, age" .)

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

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