Thrilled editor's about overdue (6)
I believe the answer is:
elated
'thrilled' is the definition.
(thesaurus)
'editor's about overdue' is the wordplay.
'editor' becomes 'ed'.
'about' means one lot of letters goes inside another.
'overdue' becomes 'late' ('late' can be similar in meaning to 'overdue').
'ed' going around 'late' is 'ELATED'.
(Other definitions for elated that I've seen before include "Very pleased, quite high" , "Over the moon" , "Feeling overjoyed and happy" , "Delighted, ecstatic" , "Jubilant, very pleased" .)