Instant cola removed from cocktail (4)
I believe the answer is:
tick
'instant' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
(Other definitions for tick that I've seen before include "Moment - parasitic arachnid" , "Blood-sucking insect or sound of old clock" , "sign of approval from teacher" , "Sound of an old watch" , "Check-mark or blood-sucking mite" .)