I solved with custom code.
This is the code of the view HikaShop - checkout / show_block_fields.php:
if(empty($this->options['read_only'])) {
$onWhat = ($oneExtraField->field_type == 'radio') ? 'onclick' : 'onchange';
$stringShippingHours = explode("select", $this->fieldClass->display(
$oneExtraField,
false,
false,
false
));
?>
<?php if($_SESSION["nField"] == 0){ ?>
<select id="orariodconsegna" name="data[order_1_4][orariodconsegna]" size="1" class="hikashop_field_dropdown hkform-control" onchange="window.hikashop.toggleField(this.value,'orariodconsegna','order_1_4',0,'hikashop_');">
<?php
foreach($stringShippingHours as $stringShippingHour){
$tz = 'Europe/Rome';
$timestamp = time();
$dt = new DateTime("now", new DateTimeZone($tz)); //first argument "must" be a string
$dt->setTimestamp($timestamp); //adjust the object to correct timestamp
$actualHour = $dt->format('H');
$nextHour = $actualHour + 1;
if($nextHour < 10){
$nextHour = '0' . $nextHour;
}
$fromNow = explode($actualHour . ':00-' . $nextHour . ':00</option>', $stringShippingHour);
echo $fromNow[1] . '<br>';
}
?>
</select>
<?php } ?>
<?php
}else{
echo $this->fieldClass->show($oneExtraField, @$cart->cart_fields->$fieldName);
}
?>