<select name="checkinMonth" class="selectform" id="checkinMonth" >
<?PHP
   for($month = $checkin_timestamp; $month <= $checkout_timestamp; $month += 30*60*60*24) {
      $checkin_month = getdate($month);
      $option_text =  strftime("%B %Y",$month);
      $option_value =  strftime("%Y%m",$month);
      $selected = ($checkin_selected == $option_value ? "selected='selected'" : "");

         echo "<option value='{$option_value}' {$selected}>{$option_text}</option>";
    }
?>
</select>