Use this snippet to set a custom time (hour, minute) for delivering all gift card scheduled for delivery on a given date:

gc-custom-delivery-time.php

<?php
/**
 * Plugin Name: WooCommerce Gift Cards - Send scheduled gift cards at a fixed time
 * Plugin URI: https://woocommerce.com/products/gift-cards/
 * Description: Use this snippet to set a custom time (hour, minute) for delivering all gift card scheduled for delivery on a given date.
 * Version: 1.0
 * Author: WooCommerce
 * Author URI: https://woocommerce.com/
 * Developer: Jason Kytros
 *
 *
 * Copyright: © 2021 Automattic
 * License: GNU General Public License v3.0
 * License URI: http://www.gnu.org/licenses/gpl-3.0.html
 */

add_filter( 'woocommerce_gc_scheduled_delivery_hour', 'sw_gc_set_scheduled_delivery_hour' );
add_filter( 'woocommerce_gc_scheduled_delivery_minute', 'sw_gc_set_scheduled_delivery_minute' );

function sw_gc_set_scheduled_delivery_hour( $hour ) {
    $hour = 0; // 0 - 23
    return $hour;
}

function sw_gc_set_scheduled_delivery_minute( $minute ) {
    $minute = 0; // 0 - 59
    return $minute;
}