I like Benchmark for such problems, e.g.

use Benchmark;
# at the beginning:
my $benchmarkStart = Benchmark->new();

# code to benchmark

# at the end:
my $benchmarkEnd = Benchmark->new();

my $diff = Benchmark::timediff($benchmarkEnd, $benchmarkStart);
my $str  = Benchmark::timestr($diff);
if ($str =~ /(\d+)\s*wallclock secs \(\s*?(\d*?\.\d*?)\s*usr\s*\+\s*(\
+d*?\.\d*?)\s/i) {
    printf ("Execution time: ~ %.0f seconds\nCPU-Time      : %.2f\n", 
+$1, $2);
}
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