I mention changes very quickly (2,2,4)
I believe the answer is:
in no time
'very quickly' is the definition.
(I've seen this before)
'i mention changes' is the wordplay.
'changes' indicates an anagram.
'mention' with letters rearranged gives 'nnotime'.
'i'+'nnotime'='IN NO TIME'
(Other definitions for in no time that I've seen before include "Very quickly" , "Very rapidly, hardly measurable" , "Immediately" , "Without delay, too quick to measure" , "Swiftly" .)