If you have the ability to cath (either a foley or a good quality external) the sub duration is pretty open ended. Otherwise you a probably looking at a max of 8-12 hours depending on age, urinary tract health etc.

Back in the Max Fisch days there was a sub who played a lot with Amanda Wildefyre. Ms Wildefyre was well known in the scene for doing extended, multi day sessions. I'm not 100% sure but I seem to recall an interview where she referenced sessions that lasted 48-72 hours.

The sub who used the screen name of -h- on MF claimed being held for something like 63 hours in a bondage bag and a similar length of time
on another occasion using a Segufix hospital restraint system. https://www.segufix-germany.com/index_en.php

No idea if it was true but he seemed legit and others on the forum (including Dommes) seemed to accept it.

My personal experience is very much less. I think my max time in isolation bondage in a bag was around 2 hours. Although, it that instance there were things done to increase discomfort so it certainly seemed longer.

When you say "extended" what sort of time frame are you considering? The longer you go the more you have to consider things like hydration, potentially some sort of nutrition (liquid?) and dealing with pressure points developing.