Second double whiskey replaced by rum with no hesitation (5)
I believe the answer is:
trice
'second' is the definition.
(both can mean a very short amount of time)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for trice that I've seen before include "Flash" , "Short time" , "Second" , "Haul" , "In a -- means very quickly" .)