To start off, I am not claiming that I understand what is expected in the final report. It looks like my code will produce different output to what others have provided.

Secondly, I should say that I have probably misunderstood what is it that you are after. I am seem to be out of tune at the moment.

Third, no attempt has been made to handle timezones.

Forth, the code will build a hash by ref number of each line in the file, so if the log is large or the available memory of the box is small, there could be problems.

Cheers.

#!/usr/bin/env perl  
use strict; use warnings;
use Data::Dumper;
use Date::Calc qw( Delta_DHMS );

my %months = (
    Jan => 1, Feb => 2, Mar => 3, Apr => 4, May => 5, Jun => 6,
    Jul => 7, Aug => 8, Sep => 9, Oct => 10, Nov => 11, Dec => 12
);

my %by_ref;
my $occured;
my @results;

push @{ $by_ref{(split)[-1]} }, do { chomp $_; $_ } while (<DATA>);

my (%p_date, $p_line, %tmdiff, %date, $r_hash);
REF:
for my $ref (keys %by_ref)
{
    next unless @{ $by_ref{$ref} } > 1;
    LINE:
    for my $line ( @{$by_ref{$ref}} )
    {
        my ($datestr, $time, $chnl) = (split /\s+/, $line)[0,1,9];
        next unless $chnl =~ /^TWO/;
        if (keys %p_date)
        {
            $r_hash = \%date;
        }   
        else
        {
            $r_hash = \%p_date;
            $p_line = $line;
        }   
        @{$r_hash}{qw/year month day hour min sec/}
            = split_date($datestr, $time);
        next unless keys %date;

        @tmdiff{qw/Dd Dh Dm Ds/}
            = Delta_DHMS( @p_date{qw/year month day hour min sec/},
                          @date{qw/year month day hour min sec/} );

        if ($tmdiff{Dd} > 0 || $tmdiff{Dh} > 0)
        {
            push @results, [ $p_line, $line ];
            $occured++;
        }   
    }   
}   
continue
{
    %date = %p_date = ();
    $p_line = "";
}
 

printf "$occured occurence%s.\n", $occured < 2 ? "" : "s";
print join("\n", @$_),"\n\n" for (@results);

sub split_date
{
    my ($datestr, $timestr) = @_;
    my @fields  = split /-/, $datestr;
    push @fields, split /:/, $timestr;
    $fields[1] = $months{$fields[1]};
    return @fields;
}

__DATA__
2008-Jan-06 00:00:01 UTC (GMT +0000) - Poll: channel = ONE, refs = 595
+166299
2007-Jan-06 00:00:01 UTC (GMT +0000) - Poll: channel = TWO, refs = 595
+159906
2007-Jan-06 00:00:01 UTC (GMT +0000) - Poll: channel = THREE, refs = 6
+59975924
2007-Jan-06 00:00:04 UTC (GMT +0000) - Poll: channel = ONE, refs = 595
+148941
2007-Jan-06 00:00:04 UTC (GMT +0000) - Poll: channel = TWO, refs = 595
+131400
2007-Jan-06 00:00:04 UTC (GMT +0000) - Poll: channel = THREE, refs = 6
+59975924
2007-Jan-06 00:00:04 UTC (GMT +0000) - Poll: channel = ONE, refs = 595
+159906
2007-Jan-06 01:00:05 UTC (GMT +0000) - Poll: channel = ONE, refs = 595
+166299
2007-Jan-06 01:00:06 UTC (GMT +0000) - Poll: channel = TWO, refs = 595
+131400
2007-Jan-06 01:00:06 UTC (GMT +0000) - Poll: channel = TWO, refs = 659
+975924
2007-Jan-06 01:00:07 UTC (GMT +0000) - Poll: channel = THREE, refs = 5
+95148941
[download]

Output;

1 occurence.
2007-Jan-06 00:00:04 UTC (GMT +0000) - Poll: channel = TWO, refs = 595
+131400
2007-Jan-06 01:00:06 UTC (GMT +0000) - Poll: channel = TWO, refs = 595
+131400
[download]