Power to restrict disorderly din at this late hour? (8)
I believe the answer is:
midnight
'this late hour?' is the definition.
'power to restrict disorderly din' is the wordplay.
'power' becomes 'might' ('might' can be a synonym of 'power'**).
'to restrict' is an insertion indicator.
'disorderly' indicates an anagram.
'din' with letters rearranged gives 'dni'.
'might' going around 'dni' is 'MIDNIGHT'.
'at' acts as a link.
(Other definitions for midnight that I've seen before include "When PM turns to AM" , "Dim thing seen at witching hour" , "Twelve o'clock" , "Twelve, perhaps" , "12am" .)