Obtaining the approval on Form I-751 is a process that takes approximately 5-12 months for most petitioners. However, processing time does vary.
First, you will receive Form I-797, Notice of Action, confirming that USCIS accepted your petition for processing. This letter will also extend your permanent resident status for an additional year, so you should carry it with you (along with your expired green card). Then you will get a biometrics appointment scheduled. This is a short appointment at a local USCIS office that includes gathering your fingerprints, photograph and signature. After biometrics screening USCIS requires you and your spouse to attend an interview with an immigration officer.
Petitioners who have not provided sufficient evidence to prove a bona fide marriage will additionally receive a request for evidence. In this case, a couple will have to prove that their marriage is not fake, fraudulent or sham.
At the end, an immigrant spouse will receive an approval notice and then a 10-year green card in the mail.