You want to use Time::HiRes.
(I altered one of the examples from the Time::HiRes docs...)

#!/usr/bin/perl
use warnings;
use strict;
use Time::HiRes qw( gettimeofday tv_interval );
# measure elapsed time 
my $t0 = [gettimeofday];
# do bunch of stuff here
my $t1 = [gettimeofday];
# do more stuff here
my $t0_t1 = tv_interval $t0, $t1;

my $elapsed = tv_interval ($t0, [gettimeofday]);
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