JSFiddle - React, Tailwind, and code Playground

JavaScript

var myTimer;
function clock() {
  myTimer = setInterval(myClock, 1000);
  var c = 60; //Initially set to 1 hour


  function myClock() {
    --c
    var seconds = c % 60; // Seconds that cannot be written in minutes
    var minutes = (c - seconds) / 60; // Gives the seconds that COULD be given in minutes
    var minutesLeft = minutes % 60; // Minutes that cannot be written in hours
    var hours = (minutes - minutesLeft) % 60;
    // Now in hours, minutes and seconds, you have the time you need.
    console.clear();
    console.log(hours + ":" + minutes + ":" + seconds)
    if (c == 0) {
      clearInterval(myTimer);
    }
  }
}

clock();