Final demand: time short in mutual wrangling (9)
I believe the answer is:
'final demand' is the definition.
(I've seen this before)
'time short in mutual wrangling' is the wordplay.
'short' means to remove the last letter.
'in' indicates putting letters inside.
'wrangling' indicates an anagram (wrangle can mean to round up and organise).
'time' with its final letter taken away is 'tim'.
'mutual' anagrammed gives 'ulatum'.
'tim' going within 'ulatum' is 'ULTIMATUM'.
(Other definitions for ultimatum that I've seen before include "Threat" , "Uncompromising demand" , "Final warning" , "Final point" , "Final statement of actions required of another" .)