Knocked back champagne with duck: time for fish (6)
I believe the answer is:
turbot
'fish' is the definition.
(I know that turbot is a type of fish)
'knocked back champagne with duck time' is the wordplay.
'knocked back' says the letters should be written in reverse.
'champagne' becomes 'brut' (I have seen 'Dry champagne ' mean 'brut' so perhaps 'champagne' could also mean 'brut').
'with' says to put letters next to each other.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'time' becomes 't' (abbreviation).
'brut' backwards is 'turb'.
'turb'+'o'+'t'='TURBOT'
'for' acts as a link.
(Other definitions for turbot that I've seen before include "Swimmer" , "Rub tot out with the fish" , "Species of fish" , "Large food fish" , "Edible flatfish" .)