Do revue, fantastic — that should have happened sooner (7)
I believe the answer is:
overdue
'that should have happened sooner' is the definition.
(something overdue should already have happened)
'do revue fantastic' is the wordplay.
'fantastic' is an anagram indicator (a fantastic or improbable ordering of the letters).
'do'+'revue'='dorevue'
'dorevue' is an anagram of 'OVERDUE'.
(Other definitions for overdue that I've seen before include "Later than expected" , "unsettled" , "not yet paid" , "Of payment, past the required date" , "Behindhand" .)