use DateTime;

use IO::All;
$temp < io($file);  

sub conv_dt {
        my ($Day,$Month,$Year,$Hour,$Minute) = @_;
        my $dt = DateTime->new(
                year      => $Year,
                month     => $Month,
                day       => $Day,
                hour      => $Hour,
                minute    => $Minute,
                second    => 0,
                time_zone => 'Europe/Berlin',
        );
        $dt->set_time_zone('UTC');
        return $dt->strftime('%d.%m.%Y %H:%M');
}

# ersetze alle Matches durch das Ergebnis von conv_dt in einem Multiline-zeichenkette
$temp =~ s/^(\d\d)\.(\d\d)\.(\d\d\d\d)\s(\d\d):(\d\d)/conv_dt($1,$2,$3,$4,$5)/egm;

$temp > io($file);