How do you know when the NVC has received your packet?

First you have to receive the NOA2 from the USCIS... then you can call the NVC hotline 1(603)334-0700 using your USCIS case number and figure out when it was received and what the new NVC case number is.

NVC sends you a letter ...and tells you when they will be sending it out...the NVC processing is quick, in and out.....so my petition
was already on its way to the embassy when i received the letter from NVC.....everything moves much faster once out
of USCIS.......good luck.....

CSC sometimes waits until they have a full shipment. Sometimes it seems they wait until they fill a cargo plane. The NVC turns the case quickly for K1s it is usually less than a week befor eit is sent off to the embassy. Once there they once again have processing rates unique to each embassy.