It's still not right though. People will say at 9pm "I did it yesterday" about something they'd done the previous date at 6pm

I don't think they're saying it can't be more than 24 hours just that it can be less.

Clearly it's confusingly worded so probably best if they just redo it.

agreed completely - "yesterday" usually includes times both greater than and less than 24 hours ago. People usually just mean… some time in the date previous to now. Roughly.

I think you switched around your sixes and nines.

I don't think I mixed it up

> No human uses “more that 24 hours” as the definition of “yesterday”. Computers, unfortunately, do.

At 9pm on Oct 14, 6pm on Oct 13 was > 24 hours ago, and people would still call it "yesterday".