if (document.getElementById('countdownTimer')) {
  pad = function(n, len) { // leading 0's
    var s = n.toString();
    return (new Array( (len - s.length + 1) ).join('0')) + s;
  };

  var timerRunning = setInterval(
    function countDown() {
      var now = new Date();
      if ( (now.getDay() >= 1) && (now.getDay() <= 5) ) { // Monday to Friday only
        var target = 17; // 15:00hrs is the cut-off point
        if (now.getHours() < target) { // don't do anything if we're past the cut-off point
          var hrs = (target - 1) - now.getHours();
          if (hrs < 0) hrs = 0;
          var mins = 59 - now.getMinutes();
          if (mins < 0) mins = 0;
          var secs = 59 - now.getSeconds();
          if (secs < 0) secs = 0;
          var str = pad(hrs, 2) + ':' + pad(mins, 2) + '.<small>' + pad(secs, 2) + '</small>';
          document.getElementById('countdownTimer').innerHTML = str;

        }
      }
    }, 1000
  );
}