public function totalMicroseconds() : int
    {
        if (null === $this->totalMicroseconds) {
            $reference = DateTime::now();
            $end       = $reference->add($this);

            $this->totalMicroseconds = $end->timestampWithMicrosecond() - $reference->timestampWithMicrosecond();
        }

        return $this->totalMicroseconds;
    }