javascriptTimer.js

<script type="text/javascript">
  setInterval("my_function('2020-04-17T18:30:00Z');",1000); 
 
    function my_function(time){
      var future = Date.parse(time)/1000;
	  var now = Date.now()/1000;
	  var totalRem = future - now;
	  var days = Math.floor(totalRem/86400);
	  var hours = Math.floor((totalRem%86400)/3600);
	  var minutes = Math.floor(((totalRem%86400)%3600)/60);
	  var seconds = Math.floor(((totalRem%86400)%3600)%60)
	  document.getElementById('time').innerHTML = days+" Days "+hours+" hours "+minutes+" Minutes and " + seconds + " seconds.";
    }

  
</script>