my $content = $response->content;
                my @network = split(/\n/,$content);
                @network = map { m/$regex/ ? $1 : ()} @network;
                ...

                foreach (@network) {
                        system("ipset add temp_$set_name $_");
                        }
[download]

You don't do any error checking on the contents of @network so why not just:

                ...

                foreach ( $response->content =~ /$regex/g ) {
                        system("ipset add temp_$set_name $_");
                        }
[download]

                system("ipset create temp_$set_name $set_type");
                foreach (@network) {
                        system("ipset add temp_$set_name $_");
                        }
                system("ipset create -exist $set_name $set_type");
                system("ipset swap temp_$set_name $set_name");
                system("ipset destroy temp_$set_name");
                my $cron_notice = "IPSet: $set_name updated (as of: $d
+ate_now).";
                system("logger", "-p", "cron.notice", $cron_notice);
[download]

You don't do any error checking on the system calls.    Perhaps something like this:

                0 == system 'ipset', 'create', "temp_$set_name", $set_
+type
                    or warn "Cannot execute ipset because: $?";
[download]

    @dates_last = $fh->getlines;
    @dates_last = map(m/^(\d+).*$/,@dates_last);
[download]

You don't really need two steps there and you don't really need .*$ at the end of the regular expression:

    @dates_last = map /^(\d+)/, $fh->getlines;
[download]

    @dates_last = split(/ /,"0 " x $urls_number)
[download]

Or just:

    @dates_last = ( 0 ) x $urls_number
[download]

          '(^([0-9]{1,3}\.){3}[0-9]{1,3}).*$', 
...
        '^(\d.*\d).*$',
...
        '(.*)',
[download]

You should compile your regular expressions here using the qr operator and the .*$ at the end is superfluous.

          qr/(^([0-9]{1,3}\.){3}[0-9]{1,3})/, 
...
        qr/^(\d.*\d)/,
...
        qr/(.*)/,
[download]

    @dates_now = map {$_ . "\n"} @dates_now;
    print $fh @dates_now;
[download]

No need for two steps:

    print $fh map "$_\n", @dates_now;
[download]

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