CPAN is your friend:

Benchmark

Time

In particular, see Benchmark and Time::HiRes. A quick and dirty solution is also the built-in time, which will give you second-level granularity, a la:

#!/usr/bin/perl
use strict;
use warnings;

my $start = time;
# Do stuff
my $duration = time - $start;
print "Execution time: $duration s\n";
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