Mean to catch on very soon? (7)
I believe the answer is:
tonight
'very soon?' is the definition.
'mean to catch on' is the wordplay.
'mean' becomes 'tight' ('tight' can be a synonym of 'mean'**).
'to catch' indicates putting letters inside.
'tight' going around 'on' is 'TONIGHT'.
(Other definitions for tonight that I've seen before include "next retirement occasion" , ""Not ____, Josephine!"" , "Dark time ahead" , "the coming time for retirement" , "after supper?" .)