The establishment in place, everyone comes in (12)
I believe the answer is:
installation
'the establishment' is the definition.
(I've seen this before)
'in place everyone comes in' is the wordplay.
'place' becomes 'station' (station is a kind of place).
'everyone' becomes 'all' (all people).
'comes in' is an insertion indicator.
'station' placed around 'all' is 'stallation'.
'in'+'stallation'='INSTALLATION'
(Other definitions for installation that I've seen before include "establishment" , "military base" , "Art exhibit in gallery" , "A setting up; equipment so set" , "Positioning" .)