Manage to retreat, getting hard time (5)
I believe the answer is:
epoch
'time' is the definition.
(epoch is a kind of time)
'manage to retreat getting hard' is the wordplay.
'manage' becomes 'cope' ('cope' can be a synonym of 'manage'**).
'to retreat' says the letters should be written backwards.
'getting' is a charade indicator (letters next to each other).
'hard' becomes 'h'.
'cope' back-to-front is 'epoc'.
'epoc'+'h'='EPOCH'
(Other definitions for epoch that I've seen before include "significant time" , "Point in time fixed by some great event" , "Unit of geological time" , "Long period of time" , "Making this date" .)