Uses IntlDateFormatter including timezone offset and DST.
see ICU Dates and Times Patterns

1. Timestamp

{{timestamp}}

/action/timestamp.php

<?php

$time        = time();
$pattern    = 'dd.MM.yyyy HH:mm'; // $this->db->date_format . ' ' . $this->db->time_format
$tpl->timestamp = $this->date_format($time, $pattern);

/action/template/timestamp.tpl

[ ' timestamp ' ]

2. Calendar week

{{cw}}

/action/cw.php

<?php

$time        = time();
$pattern    = 'ww';
$tpl->week = $this->date_format($time, $pattern);

/action/template/cw.tpl

[ ' week ' ]