Busy, cite changes in hours, constant (6)
I believe the answer is:
hectic
'busy' is the definition.
(thesaurus)
'cite changes in hours constant' is the wordplay.
'changes' indicates an anagram.
'in' is an insertion indicator.
'hours' becomes 'h'.
'constant' becomes 'c' (mathematical abbreviation).
'cite' with letters rearranged gives 'ecti'.
'h'+'c'='hc'
'ecti' put within 'hc' is 'HECTIC'.
(Other definitions for hectic that I've seen before include "in a rush" , "Frantic or feverish" , "Frenzied" , "Marked by intense activity" , "Frantically busy" .)