Coming publicity opening (6)
I believe the answer is:
advent
'coming' is the definition.
('advent' can be a synonym of 'coming')
'publicity opening' is the wordplay.
'publicity' becomes 'ad' (advert).
'opening' becomes 'vent' (vent is a kind of opening**).
'ad'+'vent'='ADVENT'
(Other definitions for advent that I've seen before include "Pre-Christmas period" , "Pre-Christmas season for Christians" , "Period in church calendar" , "when the Church year begins" , "introduction" .)