My aunt and my cousin have become residents of the US via I-485 petition by my mom. They both have their greencards and have gotten re-entry permits. They're both in China, my cousin is still attending college and her mom still has a full-time job (one more year of work). They've gone back to China 6 months at a time during the past year, only staying for a week when they come to the US, to perhaps keep the green card "alive," I guess you could say. What is the time limit they can stay out of the USA? TIA for your help.