Length of the French allotment (8)
I believe the answer is:
duration
'length' is the definition.
(I know that length can be written as duration)
'of the french allotment' is the wordplay.
'of the french' becomes 'du' ('of the' in French).
'allotment' becomes 'ration' (I've seen this in another clue).
'du'+'ration'='DURATION'
(Other definitions for duration that I've seen before include "Time scale" , "Around it (anag.)" , "Term, span, time" , "Period during which something continues" , "Length of time" .)