When does the couple have to file for marriage before it's too late for the visitor?
When a B1/B2 visitor such as yourself gets lawfully admitted into the country with an I-94, it doesn't matter, if you file for AOS thru marriage to a USC if you have been out of status for 1 month or 5. Try not to be out of status for more than 6 when filing, for you won't (should not) use an Advance Parole document to travel out of the country, for if you do, you will be triggering the 3 or 10 year bar and your spouse will need to file an extreme hardship waiver on your behalf, which grant is totally discretionary. Of course, you will not face any of that if you never leave the country until you actually obtain the green card. In such a situation, you could be out of status for years, but still be able to file for AOS as the spouse of a USC.
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
Are you a U.S. citizen? If you are, you can sponsor your spouse.
This answer is of a general nature and should not be relied upon as final, nor is it intended as legal advice. Consult with a qualified attorney before making any legal decisions. Gen Kimura, (832) 247-6932.