Schedule non-disclosure agreement after a long time (6)
I believe the answer is:
agenda
'schedule' is the definition.
('agenda' can be a synonym of 'schedule')
'non-disclosure agreement after a long time' is the wordplay.
'non-disclosure agreement' becomes 'nda' (legal abbreviation).
'after' means one lot of letters go next to another.
'a long time' becomes 'age' ('age' can be a synonym of 'long time').
'nda' after 'age' is 'AGENDA'.
(Other definitions for agenda that I've seen before include "Plan for meeting" , "Topics for a meeting" , "List of matters to be discussed at a meeting" , "plan of things to be done" , "List of items for discussion at a meeting" .)