How long before my J-1 program starts can I arrive in the United States?
你自己看这个问题，用的是before这个词，问的是在J-1开始之前多长时间能到达美国，答案当然是30天了，也就是说你最早可以比2019表规定的时间提前30天到达美国。你可以用after问这个问题看看，应该也是30天。所以应该是前后30天都是有效的。
In case of a delay and you are unable to enter the U.S. within 30 days of the initial start date of your program, as indicated on the DS-2019, you MUST notify us immediately so that we can update your DS-2019 for a later entry date. Failure to do so may cause your status to become INVALID and you may not be allowed to enter the country.
这说的很清楚，就是再晚不能超过1个月。
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maomaoyc
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