Exactly on time following the party (2,3,3)
I believe the answer is:
on the dot
'exactly' is the definition.
(I know that exactly can be written as on the dot)
'on time following the party' is the wordplay.
'time' becomes 't' (abbreviation).
'following' means one lot of letters go next to another.
'party' becomes 'do' (do is a kind of party).
'the'+'do'='thedo'
't' put after 'thedo' is 'thedot'.
'on'+'thedot'='ON THE DOT'
(Other definitions for on the dot that I've seen before include "Precisely punctual" , "at exactly the arranged time" , "Prompt" , "on precise place in line?" , "Promptly" .)