I got the 9:15, it’s a smaller one and you can’t Double Stack it. I’ll try to find a link. But it sounds the same, when the pressure goes to zero then you take the weight off. And then it says to open the lid right away, or not to wait more than 3 minutes, maybe 5 minutes, I can’t remember the exact directions.
I have the 921 and just read the instruction book.
https://www.allamericancanner.com/All-American-21-Quart-Pressure-Canner.htm
There is no advice to remove the lid quickly after it is cooled enough to remove the pressure weight. Sometimes, if I’m only doing one batch, I’ll let it cool overnight. Never had a vacuum form because the vent that the weight sits on allows air in, but also the black safety plug leaks air as well. I’ve noticed that as my canner leaks steam as it’s coming up to temperature around the black pressure relief plug. But once it’s up to pressure, that stops.
I just regularly check the temperature gauge and watch it while it’s processing. I never leave it unattended for the whole time of the canning. I’m always around listening for the rattle of the weight and occasionally checking the gauge.