I'm not 100% sure what you're trying to do. Do you want to get the files by name, or by date?

At any rate, you're on the right line with that code, but you need to check what $ftp->mdtm is returning. You could try something like this (after the cwd):

    my @d = $ftp->ls();
    for (@d) {
        my $mdtm = strftime("%Y/%m/%d %H:%M:%S", localtime($ftp->mdtm(
+$_)));
        print "filename = $_\nmdtm = $mdtm\n";
        # check file is newer than whatever criteria you have
        if ($mdtm ge "whatever") {
            $ftp->get($_);
        }
    }
[download]

Sorry if I've misunderstood your question. Hope this helps in some way...

Update: fixed the strftime format string.