Using gettimeofday and tv_interval makes it a bit simpler.

$ perl -Mstrict -Mwarnings -MTime::HiRes=gettimeofday,tv_interval -E '
my $t0 = [ gettimeofday() ];
my @psLines = qx{ ps -ef };
print
   qq{Command took },
   tv_interval( $t0, [ gettimeofday() ] ),
   qq{ seconds to run\n};'
Command took 0.015902 seconds to run
$
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I hope this is helpful.

use strict;
use warnings;
use diagnostics;

use Time::HiRes qw( time );
my $start = time();

system("program-name file-name");

my $end = time();
my $runtime = sprintf("%.16s", $end - $start);
print "This script took $runtime seconds to execute\n";
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I mean something like:

use strict;
use warnings;
use diagnostics;

use Time::HiRes qw( time );
my $start = time();
stringsNthings();
your actual code goes here;
whether it be system(whatever_prog, whatever_arg);
or
sub stringsNthings{

    my $hello_world = "hello world\n";
    my $sum = 1 + 2;
    chomp(my name = <STDIN>);
}
print stringsNthings($hello_world);
print stringsNthings($sum."\n");
print stringsNthings($name);

my $end = time();
my $runtime = sprintf("%.16s", $end - $start);
print "This script took $runtime seconds to execute\n";
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As long as you put working code in there it should time it. The code posted more than likely wont work, its just a visual example.

That measures the elapsed real time (wall clock time), not CPU time. Which do you want to measure?

Yes, Time::HiRes like posted here: http://www.perlmonks.org/?node_id=1109765