Captures user login timestamp and saves to user meta in WordPress

wp-last-login.php

<?php
/**
 * Captures user login timestamp and saves to user meta
 *
 * @param string $user_login Username of user logging in
 * @param object $user       WP_User object of user logging in
 */
add_action('wp_login', function($user_login, $user) {
	$timestamp = date('Y-m-d H:i:s', current_time('timestamp', 1));
	update_user_meta($user->ID, 'last_login', $timestamp);
}, 10, 2);

/**
 * Adds Last Login column to user list in wp-admin
 */
add_filter('manage_users_columns', function($column) {
	$column['last_login'] = 'Last Login';
	return $column;
});

/**
 * Populates Last Login column in user list in wp-admin
 *
 * @param string $output      Custom column output
 * @param string $column_name Column name
 * @param int    $user_id     ID of the currently-listed user
 */
add_filter('manage_users_custom_column', function($output, $column_name, $user_id) {
	switch ($column_name) {
		case 'last_login':
			if ($last_login = get_the_author_meta('last_login', $user_id)) {
				$last_login = get_date_from_gmt($last_login, get_option('date_format') . ' \a\t ' . get_option('time_format'));
				return esc_html($last_login);
			} else {
				return 'Unknown';
			}
			break;
		default:
	}
	return $output;
}, 10, 3);

/**
 * Styles Last Login column in user list in wp-admin
 */
function vtl_last_login_column_style() {
	echo '<style type="text/css">.column-last_login { width: 12%; }</style>';
}

add_action('admin_print_styles-users.php', 'vtl_last_login_column_style');
add_action('admin_print_styles-site-users.php', 'vtl_last_login_column_style');