We are not starting marathon soon (7)
I believe the answer is:
erelong
'soon' is the definition.
(I've seen this before)
'we are not starting marathon' is the wordplay.
'we are' becomes 'we're' (contraction of 'we are').
'not starting' means to remove the first letter.
'marathon' becomes 'long' (marathon can mean long or lengthy).
'were' with its initial letter taken off is 'ere'.
'ere'+'long'='ERELONG'
(Other definitions for erelong that I've seen before include "Soon (poetic)" , "Soon (archaic)" , "Soon (poetically)" , "Soon (arch.)" .)