You will need to use Time::HiRes to get a fine enough time granularity to do anything useful.

I while back a wrote a small script to monitor my servers for performance changes (so that I had ammo when complaining to my DSL provider). I found that the size of the page you are downloading effect the time significantly since there are fixed costs to the socket connection. Therefore I used a lower level module Net::HTTP so that I could specify a fixed download size. Here is the code snippet...

 use Time::HiRes qw(gettimeofday);

 :
 :

 my $prep_start = gettimeofday ;
 $conn = new Net::HTTP( 'Host'=>"$url") || goto END_LOOP;
 my $prep_end = gettimeofday;

 # - - - - -  Start - - - - - -
 my $start = gettimeofday ;
 $rtn = $conn->write_request(GET => "/", 'User-Agent' => "perlworks/1.
+0") || goto END_LOOP;;

 my ($code, $mess, %h) = $conn->read_response_headers();
 $data{'page_size'} = $conn->read_entity_body($page, 512);
 my $end = gettimeofday;
 # - - - - -  Stop  - - - - - -

 :
 :

 my $delta = $end - $start;
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