This code cleard the date value when you are using the plugin https://wordpress.org/plugins/woo-save-abandoned-carts/ so retained sate is not maintained for date

retain-form-value-on-checkout-page.php

<?php
/*
Make sure auto selection of date and time is disabled
https://wordpress.org/plugins/woo-save-abandoned-carts/
*/
add_action('wp_enqueue_scripts', 'pisol_clearValue');
function pisol_clearValue(){
 if(is_checkout()){
 $js = 'jQuery(function ($) {
            setTimeout(\'jQuery("#pi_delivery_date").val("")\',100);
        });';
		
  wp_add_inline_script( 'jquery', $js, 'after' );
 }
}