回复：Pjiang和大侠们请教绿卡和回美证

一家三口广州领馆签证，通过后可不可以爸爸先来，一阵子后妈妈再和儿子过来，
-可以. But all the family members have to enter U.S. before their immigration visa expires (the expiration date is indicated on the each visa).
还是一定要全家一起来？

另外，登陆后大概多久能收到绿卡？
-When they enter U.S., they become lawful permanent resident immidiately. They can file I-90 to get the physical card immidiately after they enter U.S. and may get it for a few months.
如果需要回国，保险起见，是不是可以办回美证？
-if they plan to stay outside US for > one year 从申请回美证到拿到回美证，大概需要多久时间？
-Several months. But they leave US after they do the fingerpringting and before the RP approval.