Having no duties former employee casually taking time to finish (6)
I believe the answer is:
exempt
'having no duties' is the definition.
(exempt from tax duties)
'former employee casually taking time to finish' is the wordplay.
'former' becomes 'ex'.
'employee casually' becomes 'temp'.
'taking' suggests deleting specific letters.
'time' becomes 't'.
'to finish' becomes 't' (I can't explain this - if you can you should believe this answer much more).
'temp' with 't' taken out is 'emp'.
'ex'+'emp'+'t'='EXEMPT'
(Other definitions for exempt that I've seen before include "Privileged" , "not expected to pay" , "Immune - absolve" , "Absolved" , "Grant immunity" .)