This removes the title entirely to get rid of a duplicate sentence, resolving at the same time a <h2> problem...

woocommerce_local_pickup_time_plugin_custom.php

<?php
/**
 * Remove the WooCommerce Local Pickup Time plugin checkout page select field title.
 *
 * @see https://github.com/WC-Local-Pickup/woocommerce-local-pickup-time/issues/103
 * @see https://github.com/WC-Local-Pickup/woocommerce-local-pickup-time/issues/104
 */
if ( class_exists( 'Local_Pickup_Time' ) ) {
    // Remove the default local pickup time field from the checkout page.
    remove_action( apply_filters( 'local_pickup_time_select_location', 'woocommerce_after_order_notes' ), array( Local_Pickup_Time::get_instance(), 'time_select') );
    // And add this custom one.
    add_action( apply_filters( 'local_pickup_time_select_location', 'woocommerce_after_order_notes' ), 'my_custom_time_select' );

    /**
     * Add the local pickup time field to the checkout page
     *
     * @param object $checkout The checkout object.
     */
    function my_custom_time_select( $checkout ) {
        echo '<div id="local-pickup-time-select">';

        $lpt = Local_Pickup_Time::get_instance();
        woocommerce_form_field(
            'local_pickup_time_select',
            array(
                'type'     => 'select',
                'class'    => array( 'local-pickup-time-select-field form-row-wide' ),
                'label'    => __( 'Pickup Time', 'woocommerce-local-pickup-time' ),
                'required' => true,
                'options'  => $lpt->build_pickup_time_options(),
            ),
            $checkout->get_value( 'local_pickup_time_select' )
        );

        echo '</div>';
    }
}