Extra flash (6)
I believe the answer is:
second
I believe this is a double definition.
'extra' is the first definition.
(I've seen this before)
'flash' is the second definition.
(both can mean a very short amount of time)
(Other definitions for second that I've seen before include "Further opportunity" , "Runner-up; short time" , "Next to first" , "Basic unit of time" , "Assistant in the ring" .)