Time to dispense with leader — oh no! (3)
I believe the answer is:
eek
'oh no' is the definition.
(exclamation of fear or concern)
'time to dispense with leader' is the wordplay.
'time' becomes 'week' (period of time).
'to dispense with leader' means to remove the first letter.
'week' with its first letter removed is 'EEK'.
(Other definitions for eek that I've seen before include "fearful cry" , "Cry of alarm" , "Sound of alarm" , "Expression of surprise" , "Alarmed expression" .)