Since then, has bustled about to hurry up (6)
I believe the answer is:
hasten
'to hurry up' is the definition.
(I've seen this in another clue)
'since then has bustled' is the wordplay.
I cannot really see how this works, but
'since' could be 'as' (both can mean 'because') and 'as' is found within the answer.
an anagram of 'then' is 'hten' which is located in the left over letters.
No letters remain.
This explanation may well be incorrect...
'about' acts as a link.
Can you help me to learn more?
(Other definitions for hasten that I've seen before include "Make faster" , "Speed up" , "Hurry along" , "dash" , "Act or move fast" .)