Promptly noted, hot rocks (2,3,3)
I believe the answer is:
on the dot
'promptly' is the definition.
(on the dot means precisely at the appointed time)
'noted hot rocks' is the wordplay.
'rocks' is an anagram indicator.
'noted'+'hot'='notedhot'
'notedhot' with letters rearranged gives 'ON THE DOT'.
(Other definitions for on the dot that I've seen before include "Absolutely punctual" , "Prompt" , "on precise place in line?" , "Promptly" , "at exactly the arranged time" .)