Black farm building time's forgotten (5)
I believe the answer is:
sable
'black' is the definition.
(heraldic term for black)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for sable that I've seen before include "Bales of rich fur" , "(Fur from) small carnivore" , "Black; antelope" , "Brush" , "Bales of valuable Russian fur" .)