How to edit the ctime of Django?

Question

In my Order model:

class Order(models.Model):
    order_num = models.CharField(max_length=128, unique=True)
    ctime = models.DateTimeField(auto_now_add=True)   
    uptime = models.DateTimeField(auto_now=True) 

I have ctime you see.

But in my Order's update APIView:

class OrderUpdateAPIView(UpdateAPIView):
    serializer_class = OrderSerializer
    permission_classes = [IsSuperAdminOrFinanceAdmin]
    queryset = Order.objects.all()
    lookup_field = "order_num" 

I can not edit the Order's ctime although the API return success.