Not off the mark and timed perfectly! (2,3,3)
I believe the answer is:
on the dot
'and timed perfectly' is the definition.
I can't judge whether this definition defines the answer.
'not off the mark' is the wordplay.
'not off' becomes 'on' ('on' is the opposite to 'off').
'mark' becomes 'dot' (dotting is a kind of marking).
'on'+'the'+'dot'='ON THE DOT'
Can you help me to learn more?
(Other definitions for on the dot that I've seen before include "Precisely punctual" , "At exactly the right time" , "Prompt" , "on precise place in line?" , "Sharp" .)