They will get 6 months and then you can extend for another 6 months. Sometimes in some instances (medical problems/Pregnancies of you wife where she is unable to take care of herself or needs to be cared for) I have seen extended for another 6 months, Total of 1 and 1/2 years( But there are chances of not getting approved too). For this you don't have to go to canada/mexico. But then after you can go to Canada/Mexico and extend it likewise as advised by Solitude.