How Does Marriage Affect Citizenship?
If an alien has a green card and they’re married to a U.S. citizen for three years, one can apply to petition the government to become a naturalized U.S. citizen based on the shorter three-year period. Whereas if you’re applying not because you’re married to a U.S. citizen, then you have to wait five years. In that sense, being married to a U.S. citizen does give you a benefit of having a shorter waiting period instead of five years it is only three years.
The relaxed residency requirements that are applicable for naturalization purposes only kick in once the alien applicant has been married to a U.S. citizen for three years while in green card status. It only helps the person once they accumulate the three years. So the length of time is determinative of when the application can be submitted.
If your spouse became a U.S. citizen a month before you get married, the relaxed residency requirements would not kick in quite yet because you have to wait another two years. Having a U.S. citizen spouse just a month before is not quite going to help at that stage, but it will later down the line.