Как правильно сохранить значение поля selected при использовании ($user_id)?

Здравствуйте,
Подскажите пожалуйста как правильно сохранить значение поля выбора количества часов?
Вот код ниже

add_action( 'mvx_after_shop_front', 'extra_delivery_express' );function extra_delivery_express() { global $MVX;$vendor_id = get_current_vendor_id();$vendor_delivery_express = '';$vendor_delivery_express = get_user_meta($vendor_id, '_vendor_delivery_express', true) ? get_user_meta($vendor_id, '_vendor_delivery_express', true) : $vendor_delivery_express;          $express_delivery_hour_vendor = '';          $express_delivery_hour_vendor = get_user_meta($vendor_id,'global_ex_hour_vendor' );?><div class="panel panel-default pannel-outer-heading">            <div class="panel-heading d-flex">                <h3><?php _e('', 'multivendorx'); ?></h3>            </div>            <div class="panel-body panel-content-padding form-horizontal">                <div class="mvx_media_block"><div class="form-group"><label class="control-label col-sm-3 col-md-3" for="_vendor_delivery_express"></label><div class="col-md-6 col-sm-9"><input type="hidden" name="_vendor_delivery_express" value="no"><input type="checkbox" id="myCheck" onclick="myFunction()" name="_vendor_delivery_express" value="yes"  <?php echo ($vendor_delivery_express=='yes' ? 'checked' : '');?>></div></div><div class="form-group" id="text" style="" ><label class="control-label col-sm-3 col-md-3"></label><div class="col-md-6 col-sm-9"><select name="global_ex_hour_vendor" class="form-control" value=""><option selected value=""> — выберите количество часов — </option><?php if($express_delivery_hour_vendor){?>    <option selected value="<?php echo $express_delivery_hour_vendor; ?>"><?php echo $express_delivery_hour_vendor; ?></option><?php } ?><option>1 час</option><option>2 часа</option><option>3 часа</option><option>4 часа</option><option>6 часов</option></select></div></div>                </div>            </div>        </div><script>function myFunction() {var checkBox = document.getElementById("myCheck");var text = document.getElementById("text");if (checkBox.checked == true){text.style.display = "block";text2.style.display = "block";} else {text.style.display = "none";text2.style.display = "none";}}</script> <?php }//save the field in databaseadd_action('mvx_save_custom_store', 'save_field_delivery_express', 10, 1);function save_field_delivery_express($user_id){        $vendor_delivery_express = $_POST['_vendor_delivery_express'];    update_user_meta($user_id, '_vendor_delivery_express', $vendor_delivery_express);        //?? как сохранить значение для $express_delivery_hour_vendor}