This gives you the hash I talked about (just sort of one liner):

use Data::Dumper;

use strict;
use warnings;

my %h1 = (
"index.html" => "Mon Oct 11 00:08:11 2004|12963",
"screenshot.jpg" => "Sun Oct 10 13:18:30 2004|234997",
"legal.html" => "Mon Oct 11 12:57:03 2004|13448",
"stylesheet.css" => "Mon Oct 11 13:57:28 2004|697",
"about.html" => "Mon Oct 11 00:08:08 2004|13225",
"archive.html" => "Mon Oct 11 00:08:09 2004|12872",
"postinfo.html" => "Fri Oct 1 23:49:15 2004|2457",
"contact.shtml" => "Mon Oct 11 00:09:48 2004|11366",
"services.html" => "Mon Oct 11 00:08:17 2004|14256",
"metatags.pl" => "Mon Oct 11 14:05:44 2004|28668",
"tools.html" => "Mon Oct 11 15:35:47 2004|14632",
"robots.txt" => "Sat Oct 9 03:35:15 2004|73",
"_vti_inf.html" => "Fri Oct 1 23:49:15 2004|1754",
"report.shtml" => "Mon Oct 11 00:07:03 2004|11686"
);

my $h2;
push @{$h2->{(split(/\|/, $h1{$_}))[0]}}, $_ for (keys(%h1));
print Dumper($h2);
[download]

Output:

$VAR1 = {
          'Sat Oct 9 03:35:15 2004' => [
                                         'robots.txt'
                                       ],
          'Mon Oct 11 14:05:44 2004' => [
                                          'metatags.pl'
                                        ],
          'Mon Oct 11 00:09:48 2004' => [
                                          'contact.shtml'
                                        ],
          'Mon Oct 11 00:08:08 2004' => [
                                          'about.html'
                                        ],
          'Mon Oct 11 12:57:03 2004' => [
                                          'legal.html'
                                        ],
          'Mon Oct 11 15:35:47 2004' => [
                                          'tools.html'
                                        ],
          'Fri Oct 1 23:49:15 2004' => [
                                         '_vti_inf.html',
                                         'postinfo.html'
                                       ],
          'Mon Oct 11 00:08:09 2004' => [
                                          'archive.html'
                                        ],
          'Mon Oct 11 00:08:17 2004' => [
                                          'services.html'
                                        ],
          'Mon Oct 11 00:07:03 2004' => [
                                          'report.shtml'
                                        ],
          'Mon Oct 11 00:08:11 2004' => [
                                          'index.html'
                                        ],
          'Sun Oct 10 13:18:30 2004' => [
                                          'screenshot.jpg'
                                        ],
          'Mon Oct 11 13:57:28 2004' => [
                                          'stylesheet.css'
                                        ]
        };
[download]