Move back in line at the same time (8)
I believe the answer is:
together
'at the same time' is the definition.
(synonyms)
'move back in line' is the wordplay.
'move' becomes 'go' (to go is to move).
'back' says the letters should be written backwards.
'in' means one lot of letters goes inside another.
'line' becomes 'tether' (line can mean a tether or rope).
'go' backwards is 'og'.
'og' put into 'tether' is 'TOGETHER'.
(Other definitions for together that I've seen before include "in league" , "In company or in conjunction" , "On the trot" , "as a group" , "Got there (anag.)" .)