Just FYI, it’s not entirely speculation, you can see 10 days in advance by doing the below on the Disney website:
- Hover over "My Disney Experience"
- Click "My Itinerary"
- Click "Add Plans" --> Click "Add Parks & Places"
- Change the date at the top
Doing so gives you the ability to see park hours through 9/13 (as of today), which is where the OP is getting their info regarding 6pm closings that weekend.
Obviously all park hours that far in advance are subject to change, especially with Disney’s trend of not updating them until much closer to the month in question lately.