Old-fashioned ad due to change - about time! (8)
I believe the answer is:
outdated
'old-fashioned' is the definition.
(thesaurus)
'ad due to change about time' is the wordplay.
'change' indicates anagramming the letters.
'about' means one lot of letters goes inside another.
'time' becomes 't'.
'ad'+'due'+'to'='addueto'
'addueto' is an anagram of 'outdaed'.
'outdaed' enclosing 't' is 'OUTDATED'.
(Other definitions for outdated that I've seen before include "old hat" , "Pass" , "Old-fashioned" , "Passe" , "to be ignoring fashion" .)