mypmpro-get-expiration-date-on-level-save.php

<?php //do not copy

/**
 * This recipe gets the expiration date for a member's membership when updating it from the Edit Member page
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function mypmpro_get_expiration_date_on_level_save() {

    if( ! empty( $_REQUEST['pmpro_member_edit_panel'] ) && $_REQUEST['pmpro_member_edit_panel'] == 'memberships' ){

        if( ! empty( $_REQUEST['expires'] ) && (int)$_REQUEST['expires'] ) {
            
            $user_id = (int)$_REQUEST['user_id'];

            //We may want to turn this into a timestamp or sanitize
            $expiration_date = $_REQUEST['expiration'];

            /**
             * Do something with $expiraion_date here
             */

        }
    } 
}
add_action( 'admin_init', 'mypmpro_get_expiration_date_on_level_save' );