Rubbish. Perhaps this slightly modified code will help you see what is happening more easily:

C:\>type test.pl
use Parallel::ForkManager;
my @collections = qw (col1 col2 col3 col4 col5);
my $max_tasks = 3;
$pm = new Parallel::ForkManager($max_tasks);
$|++;
my $start = time();

for my $collection (@collections) {
    my $pid = $pm->start and next;
    printf "Begin processing $collection at %d secs.....\n", time()-$s
+tart;
    sleep rand(5)+2;
    printf ".... $collection done at %d secs!\n", time()-$start;
    $pm->finish;
}

C:\>perl test.pl
Begin processing col1 at 0 secs.....
Begin processing col2 at 0 secs.....
Begin processing col3 at 0 secs.....
.... col3 done at 3 secs!
Begin processing col4 at 3 secs.....
.... col1 done at 4 secs!
Begin processing col5 at 4 secs.....
.... col2 done at 5 secs!
.... col4 done at 6 secs!
.... col5 done at 9 secs!

C:\>
[download]