Twelve using power to restrict awful din (8)
I believe the answer is:
midnight
'twelve' is the definition.
(I've seen this before)
'power to restrict awful din' is the wordplay.
'power' becomes 'might' ('might' can be a synonym of 'power'**).
'to restrict' is an insertion indicator.
'awful' indicates an anagram.
'din' anagrammed gives 'dni'.
'might' going around 'dni' is 'MIDNIGHT'.
'using' acts as a link.
(Other definitions for midnight that I've seen before include "Pitch darkness" , "Twelve o'clock" , "when PM finishes" , "12 hours from noon" , "when it's usually dark" .)