With AT&T, I cancelled Web Order on Apple.com, then called AT&T to have my eligibility reset. Once you get through to the right person/department, they do it instantly.
I would not wait for the system to do it on its own.
My first post from my X. This is the route we took. My wife and I canceled today and got ours in store pickup today. It’s pretty instant. I had a delivery date prior of December 5th.
I walked into att on launch day and they had some 64’s in stock. Tried to tell them to cancel my pre order and give me a X. They said they couldn’t cancel it and if I did, it would take a couple days to go through. I was baffled. I ended up just sticking with my pre order since it’s supposed to ship beginning of November