code: function ExcelDateToJSDate(serial) {
    var utc_days = Math.floor(serial - 25569);
    var utc_value = utc_days * 86400;
    var date_info = new Date(utc_value * 1000);
  
    var fractional_day = serial - Math.floor(serial) + 0.0000001;
  
    var total_seconds = Math.floor(86400 * fractional_day);
  
    var seconds = total_seconds % 60;
  
    total_seconds -= seconds;
  
    var hours = Math.floor(total_seconds / (60 * 60));
    var minutes = Math.floor(total_seconds / 60) % 60;
  
    return new Date(
      date_info.getFullYear(),
      date_info.getMonth(),
      date_info.getDate(),
      hours,
      minutes,
      seconds
    );
  }
docs: Converting Excel Date Serial Number to Date using Javascript
  Source: http://stackoverflow.com/a/16233621/336596
  @param {[type]} serial a date value in "Excel Date Serial" format