JSFiddle - React, Tailwind, and code Playground

HTML

<div id="time">
</div>

JavaScript

var convertTime = function(totalTime) {
  //var totalTime = 56.2332;
  var timestamp = "";

  var hour = parseInt(Math.trunc(totalTime));
  hourStr = hour < 10 ? "0" + hour.toString() : hour.toString();
  timestamp += hourStr + ":";
	
  alert(hour);
	alert(totalTime - hour);
  var min = (totalTime - hour) * 60;
  alert(min);
  min = Math.trunc(min);
  minStr = min < 10 ? "0" + min.toString() : min.toString();
  timestamp += minStr + ":";

  var sec = (totalTime - min) * 60;
  sec = Math.trunc(sec);
  secStr = sec < 10 ? "0" + sec.toString() : sec.toString();
  timestamp += secStr;
  return timestamp;
}

var convertTime_2 = function(totalTime) {
	var timestamp = "";
  
  var totalSec = totalTime * 60 * 60;
  var sec = Math.trunc(totalSec % 60);
  secStr = sec < 10 ? "0" + sec.toString() : sec.toString();
  timestamp = ":" + secStr + timestamp;
  
  var min = (Math.trunc(totalSec / 60)) % 60;
  minStr = min < 10 ? "0" + min.toString() : min.toString();
  timestamp = ":" + minStr + timestamp;
  
  var hour = Math.trunc(totalSec / (60 * 60));
  hourStr = hour < 10 ? "0" + hour.toString() : hour.toString();
  timestamp = hourStr + timestamp;
  return timestamp;
}


document.getElementById("time").innerHTML = convertTime_2(1.2);