A foreboding of this moment - about time after not starting (12)
I believe the answer is:
presentiment
'a foreboding' is the definition.
(I know that foreboding can be written as presentiment)
'this moment about time after not starting' is the wordplay.
'this moment' becomes 'present' (synonyms).
'about' means one lot of letters goes inside another.
'after' says to put letters next to each other.
'starting' indicates taking the first letters.
The initial letter of 'not' is 'n'.
'time'+'n'='timen'
'present' enclosing 'timen' is 'PRESENTIMENT'.
'of' acts as a link.
(Other definitions for presentiment that I've seen before include "Intuitive foreboding" , "An intuitive feeling" , "Feeling of apprehension" , "bad feeling" .)