wppb_toolbox_count_user_logins.php

<?php

add_action( 'wp_login', 'wppb_toolbox_count_user_logins', 20, 2 );
function wppb_toolbox_count_user_logins( $user_login, $user ) {
	if ( empty($user->ID) ) return;

	$now = new DateTime( 'now', wp_timezone() );
	update_user_meta( $user->ID, 'last_login_date', $now->format( 'Y-m-d H:i:s' ) );
}