Postpone sentence of agent brought to Rhode Island day before (8)
I believe the answer is:
reprieve
'postpone sentence of' is the definition.
(to reprieve someone is to postpone punishment)
'agent brought to rhode island day before' is the wordplay.
'agent' becomes 'rep' (short for representative).
'brought to' is a charade indicator (letters next to each other).
'rhode island' becomes 'ri' (US postal abbreviation).
'day before' becomes 'eve' (I've seen this in another clue).
'rep'+'ri'+'eve'='REPRIEVE'
(Other definitions for reprieve that I've seen before include "Temporary relief from harm" , "Save from execution" , "Delay or cancel (death sentence)" , "Postponement of the death sentence" , "Delay or cancel punishment" .)