About time, forces retreating: that's more intelligent (7)
I believe the answer is:
smarter
'more intelligent' is the definition.
('smart' can be similar in meaning to 'intelligent')
'about time forces retreating' is the wordplay.
'about time' becomes 'ret' (I've seen this in other clues).
'forces' becomes 'rams' ('ram' can be a synonym of 'force').
'retreating' says the letters should be written in reverse.
'ret'+'rams'='retrams'
'retrams' written backwards gives 'SMARTER'.
'that's' acts as a link.
(Other definitions for smarter that I've seen before include "Neater, tidier" , "More stylish" .)