Apparel below is not easy to translate, which is probably similar to posting a post in a forum. No one replies to the post, so it sinks.
priority date
1. it refers to the priority date, which is a word related to the law or (I remember it should be related to the patent law).
2. Schedule, that is, the first day when you start to apply for a green card to the government of that country. The date of that day is the number you got in line.
the second explanation should be what you need.