As of the window, although it is not explicitly stated

on the government website, at least 2 month stay after extrance is recommended. 3 month is preferred. If you start too early, your mom's intention of entering with a non-immigrant visa will be suspected.

My mom is here with me. She came to take care of me since I just had a major surgery. She has been here for almost 3 months. My dad is in China. I will have to follow different procedures to petition for their GC respectively.