In Perl if you want to calculate time in milliseconds (thousandths of a second) you can use Time::HiRes and the time() function.

use Time::HiRes qw(time);

my $start = time();

# Stuff you want to time here

my $elapsed = time() - $start;

printf("%0.2f seconds\n", $elapsed);
printf("%0.1f milliseconds\n", $elapsed * 1000);
printf("%d microseconds\n", $elapsed * 1000 * 1000);
printf("%d nanoseconds\n", $elapsed * 1000 * 1000 * 1000);