However the 5 min figure comes from my customers like DSC (R.I.P), Ericsson and Nokia building POTS switches. These guys were deadly serious, like the folks who made spacecraft and medical devices, plus the Ericsson and Nokia folks were nice too.
In DSC’s case they were so paranoid that they paid us a massive amount to maintain a special tool chain for just for them. It was frozen in time (no upgrades) and when they reported a bug and we sent them an updated tool chain they diffed the binaries and made sure that every delta was due to the big fix and nothing else (that the dev hadn’t snuck in some other patch for some reason)! They did some other headstands with their hardware and software, but in the end it didn’t save them.
It’s cool that the consent decree is online. That arrangement with the Bell system was very clever, though it led to a lot of weird anomalies and distortions but I think it did end up with a better phone system than the PTT model. It’s also been a better model than what’s happened with the power and water utilities.
The FCC back then was a better regulator for phone customers than the (now obsolete) ICC had been.