Notice express coming (6)
I believe the answer is:
advent
'coming' is the definition.
(advent is the arrival or coming of something)
'notice express' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'express' becomes 'vent' (venting is a kind of expressing).
'ad'+'vent'='ADVENT'
(Other definitions for advent that I've seen before include "Arrival - time before Christmas" , "Church season" , "Pre-Christmas season for Christians" , "Forty days preceding Christmas" , "Time approaching Christmas" .)