Preparation of cheese with some fish before midnight (8)
I believe the answer is:
briefing
'preparation' is the definition.
(thesaurus)
'cheese with some fish before midnight' is the wordplay.
'cheese' becomes 'brie' (Brie is an example).
'with' is a charade indicator (letters next to each other).
'some fish' becomes 'fin' (a fin is a part of a fish).
'before' says to put letters next to each other.
'midnight' becomes 'g'.
'brie'+'fin'+'g'='BRIEFING'
'of' acts as a link.
(Other definitions for briefing that I've seen before include "Update session" , "Issuing instructions or giving information" , "Information (meeting)" , "Act of giving instructions in advance" , "Session to give information or instructions" .)