Say more. I'm not sure if you mean mean they'll accept that even if it's not in the job posting; or if you mean they'll tolerate you working for less than you are supposed to without being above-board about it.
It's always worth talking about. I think most companies avoid putting part time explicitly on a job posting because that sends a message that this is a side gig vs. something you should be focused on. I know for sure for the right candidate I'd be open to 30 hours a week or something like that (less than 20 to be fair is where I'd probably draw the line).
I mean there's people who are barely working right now, including many people who are barely working at multiple companies and getting paid for full time employment at all of them. With that in mind, scaling back from 8 hours to 4-6 while still delivering everything you need to deliver seems very achievable. And in many places that level of commitment is the norm - everyone including management is working those reduced hours - companies just aren't spelling it out in their contracts.
