Messenger gains time as attendant (8)
I believe the answer is:
courtier
'attendant' is the definition.
(I know that courtier is a type of attendant)
'messenger gains time' is the wordplay.
'messenger' becomes 'courier' (synonyms).
'gains' is an insertion indicator.
'time' becomes 't' (abbreviation).
'courier' placed around 't' is 'COURTIER'.
'as' is the link.
(Other definitions for courtier that I've seen before include "Monarch's adviser" , "king's follower" , "Attendant on monarch" , "Monarch's companion" , "royal companion" .)