How To Create Countdown Timer dynamically using php and javascript. Your countdown will start on the page load. You can use your online exam system and many other places.

<p id="demo" style="text-align: center;font-size: 45px;margin-top: 0px;"></p>

<?php
    $examMin=1;
    $start = date('Y-m-d H:i:s');

    $nowdateM=date('Y-m-d H:i:s',strtotime('+0 hour +'.$examMin.'   minutes',strtotime($start)));
    $nowdate=strtotime($nowdateM);
    $m=date('M',$nowdate);
    $d=date('d',$nowdate);
    $y=date('Y',$nowdate);
    $time=date("H:i:s",$nowdate);
 ?>

<script>
var countDownDate = new Date("<?php echo $m; ?> <?php echo $d; ?>,<?php echo $y; ?> <?php echo $time; ?>").getTime();
var x = setInterval(function() {
   
    var now = new Date().getTime();
    var distance = countDownDate - now;
    var days = Math.floor(distance / (1000 * 60 * 60 * 24));
    var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
    var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
    var seconds = Math.floor((distance % (1000 * 60)) / 1000);
    document.getElementById("demo").innerHTML = minutes + "m " + seconds + "s ";
    if (distance < 0) {
        clearInterval(x);
       
        document.getElementById("demo").innerHTML = "EXPIRED";
    }
}, 1000);
</script>