Time to take part in operations (3)
I believe the answer is:
era
'time' is the definition.
(era is a kind of time)
'part in operations' is the wordplay.
'part in' says the answer is hidden in the clue.
'ERA' is hidden within 'operations'.
'to take' is the link.
(Other definitions for era that I've seen before include "Characteristic period" , "Eon" , "Age of importance" , "Special time" , "Distinctive period of time" .)