PM one on raft at sea (9)
I believe the answer is:
afternoon
'pm' is the definition.
(I've seen this in another clue)
'one on raft at sea' is the wordplay.
'at sea' indicates an anagram.
'one'+'on'+'raft'='oneonraft'
'oneonraft' anagrammed gives 'AFTERNOON'.
(Other definitions for afternoon that I've seen before include "Then it's early in this!" , "time for tea" , "The period following midday" , "half a day?" , "one not far out" .)