I think USCIS is delaying CR1 cases to IR1 to reduce the backlog. Once they approve your IR1, good thing is you are done with them for 10 years for GC renewal or 3 years if you chose to become citizen. Seems like case delaying has something for both parties. After watching few cases i can say 8-10 months at USCIS and the 10 to 14 months at NVC stage including interview