Dark times — but things have altered (6)
I believe the answer is:
'dark times' is the definition.
(I've seen this in another clue)
'things have altered' is the wordplay.
'things' anagrams to 'NIGHTS'.
Though, I'm not clear how this is indicated.
'but' acts as a link.
Can you help me to learn more?
(Other definitions for nights that I've seen before include "Periods after sunset" , "Times after sunset" , "Things (anag.)" , "dark times" , "Times of darkness" .)