Once I enter USA with my envelope when can I travel overseas again?

Hi, I just had my interview with the USA embassy in Tokyo. I received approval for my Green card and was mailed an envelope which I am supposed to submit to immigration on arrival in USA. From that day on 1)How long will it take until I receive my Green card in the mail?
2)Once I receive the Green card in the mail, am I allowed to go overseas again or do I need to wait a certain amount of time before I leave USA?
Thanks
 
1. Usually a few weeks
2. You don't even need to receive your plastic card to go overseas again. The moment you enter the US with your immigrant visa, you immediately become a permanent resident. The immigrant visa, stamped upon entry, automatically turns into an I-551 (green card) valid for one year. You can then take the next flight out if you want.
 
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