Are back in time (3)
I believe the answer is:
era
'time' is the definition.
(era is a kind of time)
'are back' is the wordplay.
'back' says the letters should be written in reverse.
'are' reversed gives 'ERA'.
'in' acts as a link.
(Other definitions for era that I've seen before include "quite some time" , "Important time" , "Long historic period" , "Long period of history" , "Eon" .)