As you say, your blocking is incorrect. Here's how to write that:

@t_arr = grep {
    $var3 = (split /[_.]/)[2];
    $var3 > $var1 and $var3 <= $var2;
} grep {
    !-d and $_ !~ /^\./ 
} readdir(EVT_DIR);
[download]

where I've added !-d to exclude directories. You might want to use -f instead to admit only regular files.