If B2 visa holder married a US citizen, how long does it take to get green card and can I continue to stay when my visa expired?

IN Houston about 3-4 months and San Antonio about 2-3 months, assuming all papers are complete and done right and the person is otherwise eligible.

It takes about 3 months from start to finish. And yes you can stay when your tourist visa expires.

Although someone on a B2 visa can typically adjust status if he or she gets married to a U.S. citizen, there are many things to consider before proceeding such as whether the intending immigrant has any grounds of inadmissibility that might prevent him/her from adjusting status. It typically takes six to nine months, however it could take longer. There are no guarantees. I would suggest you work with an experienced immigration attorney to guide you through this process. One mistake on your part could be costly.