From Longman Dictionary of Contemporary Englishon the doton the dotinformalTIME/AT A PARTICULAR TIME exactly on time or at a particular time I’ll be there on the dot.at three o'clock/seven thirty etc on the dot (=at exactly 3:00/7:30 etc) Mr Green arrived at six on the dot. → dot
Examples from the Corpus
arrived ... on the dot• Matthew arrived on the dot of seven. 