Date::Manip also has nice functions for manipulating dates.

#!/usr/bin/perl
use strict;
use warnings;

use Date::Manip;
use Text::CSV_XS qw( );

my $end = UnixDate("last Friday", "%Y%m%d23");
my $start = UnixDate(DateCalc("last Friday", "- 4 days"), "%Y%m%d00");

my $csv = Text::CSV_XS->new();
while (<$fh_in>) {
    $csv->parse($_)
       or die("csv: " . $csv->error_diag() . "\n");

    my ($ts) = $csv->fields();
    next if $ts lt $start || $ts gt $end;

    print $fh_out $_;
}
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