protected function getExecutionTime()
    {
        if ($this->executionTime === null) {
            $resource = $this->getActionExecution();

            if ($resource !== null) {
                /** @var \core_kernel_classes_Resource $resource */
                $time = (string) $resource->getOnePropertyValue(new \core_kernel_classes_Property(self::PROPERTY_EXECUTION_TIME));
                if (!empty($time)) {
                    $this->executionTime = new DateTime('@' . $time);
                }
            }
        }
        return $this->executionTime;
    }