Half a minute or less (5)
I believe the answer is:
minor
'less' is the definition.
(thesaurus)
'half a minute or' is the wordplay.
'half a' indicates taking half.
'minute' with half the letters taken is 'min'.
'min'+'or'='MINOR'
(Other definitions for minor that I've seen before include "Of less importance" , "Smaller - child" , "Young person below voting age" , "Of lesser importance" , "Under-age or of little importance" .)