Are you using Net::FTP? You can get the modification times with that module, then look for the file with the newest modification time. For example:

#!/usr/bin/perl

use Net::FTP;

my $ftp = Net::FTP->new('ftp.cpan.org', Debug => 1)
    or die "Couldn't connect\n";
$ftp->login('anonymous','')
    or die "Couldn't log in\n";
my $newestfile;
my $newesttime = 0;
foreach my $file ($ftp->ls)
{
  my $mdtm = $ftp->mdtm($file)
      or next;
  if ($mdtm > $newesttime)
  {
    $newestfile = $file;
    $newesttime = $mdtm;
  }
}
print "Getting file '$file'\n";
$ftp->get($newestfile);
[download]