Exact time when sentence ends (2,3,3)
I believe the answer is:
on the dot
'exact time' is the definition.
'when sentence ends' is the wordplay.
I cannot really see how this works, but
'when' could be 'on' (I've seen this in other clues) and 'on' is located in the answer.
This explanation may well be incorrect...
(Other definitions for on the dot that I've seen before include "on precise place in line?" , "Absolutely punctual" , "at exactly the arranged time" , "Prompt" , "Precisely punctual" .)