Saw notice ahead of time (5)
I believe the answer is:
adage
'saw' is the definition.
(saw can mean a proverb or saying)
'notice ahead of time' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'ahead of' means one lot of letters go next to another (some letters go in front of others).
'time' becomes 'age' (an age is a period of time).
'ad'+'age'='ADAGE'
(Other definitions for adage that I've seen before include "Slogan" , "Wise old saying" , "True proverb or saying" , "Short statement expressing a general truth" , "Old saying, maxim" .)