Representative time with book (5)
I believe the answer is:
agent
'representative' is the definition.
(agent is a kind of representative)
'time with book' is the wordplay.
'time' becomes 'age' (an age is a period of time).
'with' is a charade indicator (letters next to each other).
'book' becomes 'nt' (New Testament).
'age'+'nt'='AGENT'
(Other definitions for agent that I've seen before include "Spy; service provider" , "Person who does business on behalf of another" , "Salesman" , "Author" , "Traveller" .)