Complicated time: old invader departs (7)
I believe the answer is:
tangled
'complicated' is the definition.
(thesaurus)
'time old invader departs' is the wordplay.
'time' becomes 't' (abbreviation).
'old invader' becomes 'angle' (I've seen this before).
'departs' becomes 'd' (common abbreviation e.g. train timetables).
't'+'angle'+'d'='TANGLED'
(Other definitions for tangled that I've seen before include "Convoluted" , "Twisted into confused mass" , "Confusedly matted" , "Muddled together, complicated" , "Confusedly twisted" .)