Noisily battled chevalier for 336 hours (9)
I believe the answer is:
fortnight
'noisily battled chevalier' is the definition.
I can't tell whether this definition defines the answer.
'for 336 hours' is the wordplay.
'336' becomes 't' (I am not sure about this - if you are sure you should believe this answer much more).
'hours' becomes 'night' (I have seen 'Hours of darkness' mean 'night' so perhaps 'hours' could also mean 'night').
'for'+'t'+'night'='FORTNIGHT'
Can you help me to learn more?
(Other definitions for fortnight that I've seen before include "short period?" , "Two weeks" , "Period of time" , "couple of weeks" , "Fourteen days" .)