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'save_data_modification' => function () {
    return [
        function ($value) {
            return new DateTime( $value, 'Y-m-d\TH:i:s.u\Z' );
        },
    ];
},

$dislocation = DislocationTable::createObject();
foreach ($row as $field => $value) {
    $dislocation->set( $field, $value );
}
$dislocation->save();

   /**
    * @param mixed $value
    *
    * @return \Bitrix\Main\Type\Date|DateTime
    * @throws \Bitrix\Main\ObjectException
    */
   public function cast($value)
   {
      if (!empty($value) && !($value instanceof DateTime))
      {
         return new DateTime($value);
      }

      return $value;
   }

DislocationTable::add( $row )

        $dislocation = DislocationTable::createObject();
        foreach ($row as $field => $value) {
            if ( \in_array( $field, $this->getDatetimeFields(), true ) ) {
                $value = new DateTime( $value, 'Y-m-d\TH:i:s.u\Z' );
            }
            $dislocation->set( $field, $value );
        }
        $dislocation->save();

....

    /**
     * Получение имён полей типа Datetime
     *
     * @return array
     * @throws ArgumentException
     * @throws SystemException
     */
    protected function getDatetimeFields(): array
    {
        $datetimeFields = [];
        $fields = DislocationTable::getEntity()->getFields();
        foreach ($fields as $field) {
            if ( $field instanceof DatetimeField ) {
                $datetimeFields[] = $field->getName();
            }
        }
        return $datetimeFields;
    }

$fields = array_map( function ($value) {
    return $value instanceof DateTime ? $value->toString() : $value;
}, $fields );

BX.ajax.runAction()

/**
 * @return array
 * @throws \Exception
 */
public function getAction(): array
{
    $rows = [];

    $dislocations = DislocationTable::getList()->fetchCollection();
    foreach ($dislocations as $dislocation) {
        $fields = array_filter( $dislocation->collectValues() );
        $rows[] = $fields;
    }

    return [
        'rows' => $this->convertKeysToCamelCase( $rows ),
    ];
}

if ($data instanceof DateTime)
{
   return date('c' , $data->getTimestamp());
}