One not far off for part of the day (9)
I believe the answer is:
afternoon
'for part of the day' is the definition.
(I've seen this before)
'one not far off' is the wordplay.
'off' indicates anagramming the letters.
'one'+'not'+'far'='onenotfar'
'onenotfar' is an anagram of 'AFTERNOON'.
(Other definitions for afternoon that I've seen before include "several hours" , "Latter part of daylight hours" , "Midday to evening" , "PM includes this" , "Between noon and evening" .)