I assume you mean the session's "till-time"? I mean, I can't find anything closer to that...
Using my client (see my signature), you can do it like so:
<?php
namespace PEAR2\Net\RouterOS;
require_once 'PEAR2/Net/RouterOS/Autoload.php';
$client = new Client('192.168.0.1', 'admin', 'password');
header('Content-Type: text/plain');//This is just to get nice text formatting...
foreach ($client->sendSync(new Request('/tool user-manager session print'))->getAllOfType(Response::TYPE_DATA) as $response) {
echo 'User: ', $response->getArgument('user'), "\nEnd time: ", $response->getArgument('till-time'), "\n\n";
}
(assuming you want this for all users)