Envoy, say, entering behind schedule (6)
I believe the answer is:
legate
'envoy' is the definition.
(legate is a kind of envoy)
'say entering behind schedule' is the wordplay.
'say' becomes 'eg'.
'entering' is an insertion indicator.
'behind schedule' becomes 'late' (I've seen this before**).
'eg' put within 'late' is 'LEGATE'.
(Other definitions for legate that I've seen before include "Emissary representing the Pope" , "Official representative" , "messenger for the Pope" , "Papal envoy from Galtee" , "Envoy - pope's representative" .)