my $timeBegin = ....; # ???
my $timePeriod = '';

while (1) {
   $timePeriod = ...; # ???

   sleep 5;
}

$b=time();
print "BEGIN $b\n";
while(1){
   $c=time()-$b;
   print "CURR $c\n";
   sleep 3;
}

use Time::HiRes qw(gettimeofday tv_interval);

my $t0 = [gettimeofday];

sleep 1;

print 'elapsed '. tv_interval( $t0 ) ."\n";