Gotcha. So this would be your recommended way to go?

    protected function write(array $record)
    {        
        // Convert the date to a MongoDate
        if (isset($record['formatted']['datetime']))
        {
            $arrTime = explode('.', $record['formatted']['datetime']); 
            $record['formatted']['datetime'] = new \MongoDate($arrTime[0], $arrTime[1]);
        }
    
        $this->mongoCollection->save($record['formatted']);
    }
    
    /**
     * {@inheritDoc}
     */
    protected function getDefaultFormatter()
    {
        // Convert date to a timestamp
        return new NormalizerFormatter('U.u');
    }