If you insist on treating e-mail as a medium requiring immediate response, you'll be going into Postfix on weekends to force-flush the queue instead. This is not a technological problem, definitely not one that's solvable through configuration tweaking.
(I mean, sure, it's an impressive exercise in how flexible the sw stack is, but the issue lies elsewhere)
If anyone expends as much effort at delivery (7 days, usually, with spaced repetition) of anything these days, I'd be seriously impressed.
> Implementing "quiet hours as seen in IM", means using the wrong tool.
Modern MUAs can usually do this sort of thing, tbf.
AFAICT using the MTA is a great way to avoid "can't stop looking syndrome"... I can't see the content of e-mails if all I see is 'rejected email from xyz@foo.bar' in the logs. Ofc, you need to reject them before they enter the queue -- that's the point!
Anyway, I don't particularly begrudge anybody solving problems in a way that works for them.
I mean, I do battle with notification-FOMO as much as anyone; if it works, go for it. I would just be tempted to poke at the rejected queue.