There are two big cut down days for NFL teams this year.
One is on August 30, and then the big cut down day is September 3, when all teams need to be down to their 53 man roster.
Originally, teams were supposed to get down to 75 players on August 30. The NFL announced that number has been raised to 80, presumably to give teams more leeway because of the abbreviated offseason.
This was essentially done so that more players would be available to use and evaluate in the often-useless fourth preseason week.
The preseason wraps up for 30 teams on September 1. The Raiders and Seahawks play on September 2.