They never said that the 72 hours were tied to the date of august 31 but to the official release. At this time, the release was scheduled for august without more precision.
Official release is : august 3. So the 72 hours apply to this date.
Speaking of august 31 is a mistake because it does not exist anymore. There is nothing at this date. The release was fixed earlier to avoid Starfield, not to grant access to an early access of 4 weeks with full content. It is not a gift, it's only the release date they have chosen. It does not change anything about the fact that they sold 72 hours early game when the game will be available. If the game is available august 3, the 72 hours begin july 31. If it is august 31 the it begins 3 days before. On PS5 the release is fixed september 6, so the 72 hours period begins the 3rd.
