It's futile going back in time, so it often appears (6)
I believe the answer is:
otiose
'it's futile' is the definition.
(synonyms)
'going back in time so it often appears' is the wordplay.
'going back' shows that the letters should be reversed in order.
'in' indicates the answer is hidden within the clue.
'esoito' is hidden within 'time so it often appears'.
'esoito' written backwards gives 'OTIOSE'.
(Other definitions for otiose that I've seen before include "Serving no useful purpose" , "Slothful" , "Without practical purpose" , "Lazy, idle" , "Disinclined to work or exert oneself" .)