Short seer unexpectedly on time (5)
I believe the answer is:
terse
'short' is the definition.
(synonyms)
'seer unexpectedly on time' is the wordplay.
'unexpectedly' indicates anagramming the letters.
'on' is a charade indicator (letters next to each other).
'time' becomes 't' (abbreviation).
'seer' is an anagram of 'erse'.
'erse' after 't' is 'TERSE'.
(Other definitions for terse that I've seen before include "Short and succinct" , "Curt among trees" , "Short, abrupt" , "Using few words" , "Trees (anag.)" .)