Won't shed rot without covers? Precisely (2,3,3)
I believe the answer is:
on the dot
'precisely' is the definition.
(on the dot can mean at a precise time)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for on the dot that I've seen before include "Promptly" , "Absolutely punctual" , "At precisely the right time" , "at exactly the arranged time" , "Sharp" .)