Need curious changes after a while (2,3,6)
I believe the answer is:
in due course
'after a while' is the definition.
(thesaurus)
'need curious changes' is the wordplay.
'changes' indicates an anagram.
'need'+'curious'='needcurious'
'needcurious' with letters rearranged gives 'IN DUE COURSE'.
(Other definitions for in due course that I've seen before include "at the proper time" , "When the time comes" , "Eventually" , "At the appropriate time" , "in the natural order" .)