After you file the I-140 Petition for Alien Relative, it takes USCIS about 5 months to complete processing. The case is then sent to the State Department’s National Visa Center (NVC). NVC takes about 3 months to complete processing at which time the case is sent to a U.S. Consulate in your wife’s home country for her interview. It usually takes approximately 2 months before an interview is set after NVC completes processing. You should plan that it will take anywhere between 10 and 12 months for your wife to have her interview and obtain an Immigrant Visa to allow her to come to the U.S.