I checked the Visa Status by using the case number and I see the same message. "at NVC" I don't really know how long will it take to be in transit but I will be optimistic and say about 2 weeks. ( I am trying to expedite because my residence permit expires soon. I am informed that the consulate will decide if they can expedite or not. )
I guess invoice number is needed to pay the fee before the appointment. But I am not sure. It's interesting that you didn't receive invoice number. But I am sure if that's a mistake, they will correct it soon.