What follows a do, back in time (3)
I believe the answer is:
era
'time' is the definition.
(era is a kind of time)
'what follows a do back' is the wordplay.
I cannot really see how this works, but
'a' is found in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for era that I've seen before include "Aeon" , "Long historical period" , "Special time" , "Are involved in time span" , "Specific time" .)