Heads of Danish unions getting allowance for a length of time (8)
I believe the answer is:
duration
'length of time' is the definition.
(I've seen this before)
'heads of danish unions getting allowance' is the wordplay.
'heads of' says to take the initial letters.
'getting' means one lot of letters go next to another.
'allowance' becomes 'ration' (I've seen this before).
The initial letters of 'danish unions' is 'du'.
'du'+'ration'='DURATION'
'for a' acts as a link.
(Other definitions for duration that I've seen before include "Time scale" , "Term, span, time" , "Length of time" , "Period during which something continues" , "Around it (anag.)" .)