The latest models, with the right setup, can already substitute for many (not all) tasks in knowledge jobs such as graphic design, support chat, even programming. I feel like we may be looking at less than 3 or 4 years for a lot of jobs to be mostly obsolete. Or at least, the traditional version of those jobs.
It's already at the point where you start expecting any knowledge worker to be significantly more productive by leveraging these tools.
It's hard to imagine that it will be more than five years before AI tools are available that can handle almost all tasks in these types of jobs.
For example, on my website aidev.codes I just added preliminary knowledgebase support. It can reference the knowledgebase this to write code. I would say that with the code-davinci-002 model at least it seems about at the level of a junior software engineer already since it's pretty effective with close supervision by a senior peogrammer, except for the fact that it cannot interpret visual information.
Knowledgebases/embedding search can also be used right now with these models for answering support questions. The only thing holding it back from very very wide scale adoption is the problem of making up information. There are already solutions in progress for this. It's unlikely that will take more than a few years to roll out and replace the current generation of models. Google and Microsoft will probably roll out their internet-scale chat search interfaces this year even if they can't fully mitigate the hallucination problem immediately.
I would guess more like 2-3 years for many knowledge-based jobs. If you want employment/contracts you will need to be very good at leveraging AI, or people will just use the AIs instead.