Painfully sensitive flesh lasting a short time (5)
I believe the answer is:
quick
'short time' is the definition.
'quick' can be an answer for 'short' (thesaurus). I am not sure about the 'time' bit.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for quick that I've seen before include "Speedy" , "living" , "Fast; alive" , "Rapid" , "Prompt; intelligent" .)