Time to stop evil lasting forever (8)
I believe the answer is:
immortal
'lasting forever' is the definition.
(immortal means living or lasting forever)
'time to stop evil' is the wordplay.
'time' becomes 't' (abbreviation).
'to stop' indicates putting letters inside.
'evil' becomes 'immoral' (evil can mean immoral).
't' placed within 'immoral' is 'IMMORTAL'.
(Other definitions for immortal that I've seen before include "Not subject to death" , "Enduring" , "Undying" , "Deathless" , "Imperishable" .)