Countdown

<div id="clockdiv">
  <div id="days">
    <span class="days"></span>
    <div class="smalltext">Дней</div>
  </div>
  <div id="hours">
    <span class="hours"></span>
    <div class="smalltext">Часов</div>
  </div>
  <div id="minutes">
    <span class="minutes"></span>
    <div class="smalltext">Минут</div>
  </div>
  <div id="seconds">
    <span class="seconds"></span>
    <div class="smalltext">Секунд</div>
  </div>
</div>

<script type="text/javascript">
  function getTimeRemaining(endtime) {
    var t = Date.parse(endtime) - Date.parse(new Date());
    var seconds = Math.floor((t / 1000) % 60);
    var minutes = Math.floor((t / 1000 / 60) % 60);
    var hours = Math.floor((t / (1000 * 60 * 60)) % 24);
    var days = Math.floor(t / (1000 * 60 * 60 * 24));
    return {
    'total': t,
    'days': days,
    'hours': hours,
    'minutes': minutes,
    'seconds': seconds
    };
  }

  function initializeClock(id, endtime) {
    var clock = document.getElementById(id);
    var daysSpan = clock.querySelector('.days');
    var hoursSpan = clock.querySelector('.hours');
    var minutesSpan = clock.querySelector('.minutes');
    var secondsSpan = clock.querySelector('.seconds');

    function updateClock() {
    var t = getTimeRemaining(endtime);

    daysSpan.innerHTML = t.days;
    hoursSpan.innerHTML = ('0' + t.hours).slice(-2);
    minutesSpan.innerHTML = ('0' + t.minutes).slice(-2);
    secondsSpan.innerHTML = ('0' + t.seconds).slice(-2);

    if (t.total <= 0) {
      clearInterval(timeinterval);
    }
    }

    updateClock();
    var timeinterval = setInterval(updateClock, 1000);
  }
  var deadline="January 01 2018 00:00:00 GMT+0300" 
  or
  var deadline = new Date(Date.parse(new Date()) + 15 * 60 * 1000);    
  //15 - минут до завершения 
  

  initializeClock('clockdiv', deadline);
</script>