[Akex]

You are in the good way

Just put this in your code :

$user['lastactivity_date'] = vbdate($vbulletin->options['dateformat'], $user['lastactivity']);
$user['lastactivity_time'] = vbdate($vbulletin->options['timeformat'], $user['lastactivity']);

Then put $user[lastactivity_date] and $user[lastactivity_time] in showgroup_usergroupbit template .

Not tested it, but I think it will work.