4 ms·There is a provision for negative leap seconds. In practice, this has never happened.by Nekhrimah 4y agoThere is a provision for negative leap seconds. In practice, this has never happened.elfchief 4y agoHasn't happened, but it may actually happen in the next half-decade or so. If not, it's almost guaranteed to happen ~25 years from now.mulmen 4y agoThanks, I skimmed the wiki and it sounded like they could only be added.