#!/usr/bin/perl
use strict;
use warnings;
use Date::Calc 'Date_to_Time';

my $command='VBoxManage.exe modifyvm "NameDerVM" --biossystemtimeoffset %u';
my $date='14.10.2011';

my $time=time();
$time-=Date_to_Time(reverse(split(/\./,$date)),0,0,0);
$time*=1000;

$command=sprintf($command,$time);

exec($command) or die(qq[ERROR exec "$command" ($!)\n]);
die("Something went wrong!\n");