Works for me. Perhaps your code doesn't take long to run??

use Benchmark;

$start = new Benchmark;

1 for 1..10000000;

$end = new Benchmark;
$diff = timediff($end, $start);
print "<p>Time taken was ", timestr($diff, 'all'), " seconds\n"; 
__END__

$ perl585 /tmp/p2
<p>Time taken was  4 wallclock secs ( 4.28 usr  0.01 sys +  0.00 cusr 
+ 0.00 csys =  4.29 CPU) seconds
$
[download]

Dave.