Evening things out, removing wrinkles at last (5)
I believe the answer is:
night
'evening things out' is the definition.
'night' can be an answer for 'evening' (I've seen this in another clue). I'm unsure of the 'things out' bit.
'removing wrinkles at last' is the wordplay.
'removing wrinkles' becomes 'nigh' (I can't explain this - if you can you should give a lot more credence to this answer).
'last' says to take the final letters.
The final letter of 'at' is 't'.
'nigh'+'t'='NIGHT'
(Other definitions for night that I've seen before include "'She walks in beauty, like the . . . . .' (Byron)" , "period of gloom" , "follow-up to 16 [TWILIGHT]" , "What proverbially follows day" , "Illumination needed now" .)