I had turned up after time -- that's swell (6)
I believe the answer is:
dilate
'swell' is the definition.
(I've seen this before)
'i had turned up after time' is the wordplay.
'i had' becomes 'id' (I'd).
'turned up' shows that the letters should be reversed in order.
'after time' becomes 'late' (I've seen this before).
'id' reversed gives 'di'.
'di'+'late'='DILATE'
'that's' acts as a link.
(Other definitions for dilate that I've seen before include "Swell" , "Become wider, pupil of the eye perhaps" , "Widen in detail as pupils may" , "explain more fully" , "Make or become wider" .)