回複：有個很菜的關於EAD問題，

If you register some official form (dont remember the form number, maybe I-9?) then the date will be counted as the beginning date.

When you start using EAD, you switch from any nonimmigrant status to AOS, which is unreversable, meaning in the unfortunate rare case I-485 got denied, you sole status at that time - AOS is gone and you cannot go back to nonimmigrant status any more, so you wouldn't have any legal status to stay in US in that situation. So, it's a wise decision to keep another status in addition to AOS.