Time flies — in small amounts (6)
I believe the answer is:
This might be a double definition.
'time flies' is the first definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Perhaps you can see an association between them that I can't see?
'small amounts' is the second definition.
(I've seen this in another clue)
'in' acts as a link.
Can you help me to learn more?
(Other definitions for traces that I've seen before include "Vestiges (that may be kicked over?)" , "Follows or discovers by examining evidence" , "Signs in crates" , "Finds; small quantities" , "Finds; hints" .)