My father visited USA first time on green card on 22 June 2018 and returned on 23 July 2018 to India to attend personal works and disposal of property. How many months he can stay in India presently to keep the green card valid. It is already nearly 3 months lapsed please let me know whether my father's green card is valid and up to what time it is valid. Is there any procedure to keep it valid. Kindly let us know with all details.