No archdeacon wants a form of worship lasting days (6)
I believe the answer is:
novena
'form of worship lasting days' is the definition.
(prayers over nine days)
'no archdeacon wants a' is the wordplay.
'archdeacon' becomes 'ven' (abbreviation for The Venerable).
'wants' says to put letters next to each other.
'no'+'ven'+'a'='NOVENA'
(Other definitions for novena that I've seen before include "Nine-day ritual" , "Special prayers offered on nine successive days" , "Devotion with prayers on nine successive days" , "Catholic nine-day devotion" , "Sequence of prayers" .)