需要倒数计时器脚本，该脚本从特定时间开始并在特定时间结束，并且在该时间之间每15分钟重置一次

Question

我已经尝试了很多脚本，但结果不是按要求提供的。

<script>
// Set the date we're counting down to
//var countDownDate = new Date("<?php echo $final_date; ?>").getTime();
var countDownDate = new Date("<?php echo $final_date; ?>").getTime();

// Update the count down every 1 second
var x = setInterval(function() {

  // Get todays date and time
  //var now = new Date().getTime();
  //alert(now);

  var offset = -7;
  var get = new Date( new Date().getTime() + offset * 3600 * 1000).toUTCString().replace( / GMT$/, "" );
  var now = new Date(get).getTime();
  //alert(now);



  // Find the distance between now an the count down date
  var distance = countDownDate - now;

  // Time calculations for days, hours, minutes and seconds
  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);

  // Output the result in an element with id="demo" 
  if(days == '0'){
    document.getElementById("demo").innerHTML = hours + "hours "
+ minutes + "minutes " + seconds + "seconds ";
  } else if(hours == '0') {
    document.getElementById("demo").innerHTML = minutes + "minutes " + seconds + "seconds ";

  } else if(minutes == '0') {
    document.getElementById("demo").innerHTML = seconds + "seconds ";

  } else if(seconds == '0') {
    document.getElementById("demo").innerHTML = "";

  } else {
    document.getElementById("demo").innerHTML = days + "days " + hours + "hours "
    + minutes + "minutes " + seconds + "seconds ";
  }

  // If the count down is over, write some text 
  if (distance < 0) {
    clearInterval(x);
    document.getElementById("demo").innerHTML = "expired";



  }
}, 1000);
</script>