To finish a voluntary on the organ, takes time (4)
I believe the answer is:
year
'time' is the definition.
(I know that time can be written as year)
'to finish a voluntary on the organ' is the wordplay.
'to finish' suggests the final letters.
'on' says to put letters next to each other.
'the organ' becomes 'ear' (the ear is an organ).
The final letter of 'voluntary' is 'y'.
'y'+'ear'='YEAR'
'takes' is the link.
(Other definitions for year that I've seen before include "Division of school" , "eg 2004" , "TV advert" , "1% of a century" , "Group of students" .)