Saw notice on time (5)
I believe the answer is:
adage
'saw' is the definition.
(saw can mean a proverb or saying)
'notice on time' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'on' is a charade indicator (letters next to each other).
'time' becomes 'age' (an age is a period of time).
'ad'+'age'='ADAGE'
(Other definitions for adage that I've seen before include "Old saw" , "Old saying; proverb" , "Proverb expressing a general truth" , "Dictum" , "Maxim, aphorism" .)