At one point in time, managers will send out 1:1 invites.
If it's like in the previous layoff, it will be around 7:00am on Mon Sep 16. For other layoffs I remember, 1:1s have been sent out on a Sat for a Mon 1:1.
Starting Sat Sep 14, I intend to monitor my manager's outlook calendar for Monday. If I see 15 min invites, and I did not get one at the same time, then I will conclude I'm save.
I don't think I have any other things to do on the weekend preceding the layoff announcement.