Consents but is a long time coming round again (6)
I believe the answer is:
agrees
'consents' is the definition.
(agreeing is a kind of consenting)
'a long time coming round again' is the wordplay.
'a long time' becomes 'ages' (ages can mean a very long time).
'coming round' is an insertion indicator.
'again' becomes 're' (prefix meaning 'again').
'ages' enclosing 're' is 'AGREES'.
'but is' acts as a link.
(Other definitions for agrees that I've seen before include "Accedes or concurs" , "Grease (anag.)" , "Is of one mind" , "Assents, concurs" , "Holds the same opinion" .)