回複：回複：Further suggestion ...

You are right. You need to take the mailing time and potential delivery risk into the consideration and leave enough time space for mailing. Your attorney should tell you the tracking number of your mail after he/she sends out your package.

Regarding your last question, please read the following comment:

(Information source: http://www.*****/ym_article/hooyou/23588532.html)

有關這些重要日期，移民局是以申請人提交申請的日期為準還是他們收到申請的日
期為準？
根據移民局最近給美國移民律師協會的一份備忘錄，這些日期是以你提交申請的時間為
準，包括郵戳、或者是FedEx, UPS or DHL的收據。但是，我們還是建議你確保將你的
申請在最後期限之前送到移民局，以防移民局的收件工作人員出錯