Time to regret being loyal (4)
I believe the answer is:
true
'loyal' is the definition.
(I've seen this before)
'time to regret' is the wordplay.
'time' becomes 't' (abbreviation).
'to regret' becomes 'rue' (to rue something is to regret it).
't'+'rue'='TRUE'
'being' is the link.
(Other definitions for true that I've seen before include "Bona fide" , "Genuine, loyal" , "Real; accurate" , "Accurate, factual" , "Unfeigned" .)