It's unusual to turn up right on time (4)
I believe the answer is:
rare
'it's unusual' is the definition.
(thesaurus)
'turn up right on time' is the wordplay.
'turn up' says the letters should be written in reverse.
'right' becomes 'r' (common abbreviation).
'on' means one lot of letters go next to another.
'time' becomes 'era' (I've seen this before**).
'r' put after 'era' is 'erar'.
'erar' reversed gives 'RARE'.
'to' acts as a link.
(Other definitions for rare that I've seen before include "Not well done!" , "Very scarce, like undercooked steak" , "Especially good" , "Unusual(ly fine)" , "difficult to find?" .)