Valued time invested in costly reversal (5)
I believe the answer is:
rated
'valued' is the definition.
(rating is a kind of valuing)
'time invested in costly reversal' is the wordplay.
'time' becomes 't'.
'invested in' is an insertion indicator.
'costly' becomes 'dear' ('dear' can be a synonym of 'costly').
'reversal' shows that the letters should be reversed in order.
't' placed within 'dear' is 'detar'.
'detar' reversed gives 'RATED'.
(Other definitions for rated that I've seen before include "Had a high opinion of" , "Estimated, set at" , "Was worthy of" , "Tread (anag.)" , "Assessed; merited" .)