CODE EXAMPLE FOR JAVASCRIPT

countdown timer javascript stack overflow

var hms = "02:30:00";
	var a = hms.split(':'); // split it at the colons

	// minutes are worth 60 seconds. Hours are worth 60 minutes.
	var seconds = (+a[0]) * 60 * 60 + (+a[1]) * 60 + (+a[2]); 

		if(seconds > 0)
		{	

	      function secondPassed() {
	      	  
	      	  
	          var minutes = Math.round((seconds - 30)/60),
	              remainingSeconds = seconds % 60;
                   var hour   =Math.floor((minutes)/60);
                    minutes = minutes%60;

	          if (remainingSeconds < 10) {
	              remainingSeconds = "0" + remainingSeconds;
	          }
              hour = ("0" + hour).slice(-2);
              minutes = ("0" + minutes).slice(-2);
              remainingSeconds= ("0" + remainingSeconds).slice(-2);

	          document.getElementById('countdown').innerHTML = hour +":" +minutes + ":" + remainingSeconds;
	          if (seconds == 0) {
	              clearInterval(countdownTimer);
	             //form1 is your form name
	            document.form_quiz.submit();
	          } else {
	              seconds--;
	          }
	      }
	      var countdownTimer = setInterval('secondPassed()', 1000);

	      }