Encouraging period of work penning most of Disney film (9)
I believe the answer is:
stimulant
'encouraging' is the definition.
(thesaurus)
'period of work penning most of disney film' is the wordplay.
'period of work' becomes 'stint' (stint can mean a period or shift of work).
'penning' indicates putting letters inside.
'most of' means to remove the last letter.
'disney film' becomes 'Mulan' (Mulan is a Disney film).
'mulan' with its last letter removed is 'mula'.
'stint' placed around 'mula' is 'STIMULANT'.
(Other definitions for stimulant that I've seen before include "Booster" , "Energizer" , "Increasing vital action" , "Reviver" , "Tonic, pick-me-up" .)