Homelion, mktime
strtotime
time
date
$time = time(); // 1370190762 (2.06.2013 19:32)
$fivemin = 5*60;
echo date('H:s', $time-$fivemin);или
$date = date('d-m-Y H:i:s', time()); // 2.06.2013 19:32
$strtime = strtotime($date); // 1370190762
$time = $srttime-$fivemin;
echo date('H:i', $time);