Time to nag about a dynasty (4)
I believe the answer is:
tang
'a dynasty' is the definition.
(Chinese dynasty)
'time to nag about' is the wordplay.
'time' becomes 't' (abbreviation).
'to' means one lot of letters go next to another.
'about' is an anagram indicator.
'nag' with letters rearranged gives 'ang'.
't'+'ang'='TANG'
(Other definitions for tang that I've seen before include "Distinctive taste" , "Strong taste; Chinese dynasty" , "The biting flavour of seaweed" , "Strong, pungent taste" , "Savour" .)