Within half a second the guys are getting better (2,3,4)
I believe the answer is:
on the mend
'are getting better' is the definition.
(on the mend means recovering from illness)
'within half a second the guys' is the wordplay.
'within' is an insertion indicator.
'half a' suggests halving the letters.
'guys' becomes 'men' (guy can mean a man).
'second' cut in half is 'ond'.
'the'+'men'='themen'
'ond' going around 'themen' is 'ON THE MEND'.
(Other definitions for on the mend that I've seen before include "undergoing recovery?" , "Looking up" , "Informally getting better, improving after illness or accident" , "Making recovery" , "Improving in health" .)