my $hour_span = DateTime::Span->from_datetimes(
            start => $dt, end => $dt
        );
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should be

        my $hour_span = DateTime::Span->from_datetimes(
            start => $dt, before => $dt->clone()->add( hours => 1 ),
        );
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or the more readable

        my $hour_span = DateTime::Span->new(
            start => $dt, hours => 1,
        );
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Update: No, neither fix help. They were suppose to make the following match:

2010-10-10 01:59:59|2010-10-10 01:59:59|blablalblabla
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You need

sub hour_in_range {
    my ($dt_s, $dt_e, @hours) = @_;

    my $dt_span = DateTime::Span->from_datetimes(
        start => $dt_s, end => $dt_e
    );

    for my $hour (@hours) {
        my $dt = $dt_s->clone()
                      ->truncate( to => 'day' )
                      ->add( hours => $hour );

        my $dt_tomorrow = $dt->clone()->add( days => 1 );

        my $hour_span = DateTime::Span->new(
            start => $dt, hours => 1
        )->union( DateTime::Span->new(
            start => $dt_tomorrow, hours => 1
        ));

        return 1 if $dt_span->intersects($hour_span);
    }

    return 0;
}
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And there you go, the four DateTimes per hour I mentioned earlier.