($YY, $MM, $DD, $hh, $mm) = ($dtstamp =~ /(\d\d\d\d)(\d\d)(\d\d)(\d\d)(\d\d)/);
$period1 =sprintf("%02d/%02d/%04d %02d:%02d",
                 $MM, $DD, $YY, $hh, $mm+15);
$period2 =sprintf("%02d/%02d/%04d %02d:%02d",
                 $MM, $DD, $YY, $hhm2, $hm2-$hhm2*60);

$period3 =sprintf("%02d/%02d/%04d %02d:%02d",
                 $MM, $DD, $YY, $hh, $mm);


$period4 =sprintf("%02d/%02d/%04d %02d:%02d",
                 $MM, $DD, $YY, $hhm2, $hm2-(($hhm2*60)-15));