Abandon work after dark on a regular basis (4)
I believe the answer is:
drop
'abandon' is the definition.
(I've seen this before)
'work after dark on a regular basis' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'after' says to put letters next to each other.
'on a regular basis' means one should take alternating letters.
The alternating letters of 'dark' are 'dr'.
'op' put after 'dr' is 'DROP'.
(Other definitions for drop that I've seen before include "Shoot" , "Small quantity of liquid" , "Wee dram" , "Dispense with - sink" , "Discontinue; sink" .)