my $start = DateTime->new(
    day       => 1,
    month     => 1,
    year      => 2009,
    hour      => 0,
    minute    => 0,
    second    => 0,
    time_zone => 'Europe/Berlin',
);

my $end = DateTime->new(
    day       => 2,
    month     => 1,
    year      => 2009,
    hour      => 0,
    minute    => 0,
    second    => 0,
    time_zone => 'Europe/Berlin',
);

print $end->delta_ms($start)->in_units('hours'), "\n";