I dont understand why the item page shows “5 hours ago”, but if you filter by domain : https://news.ycombinator.com/from?site=sivers.org, the same item is labeled “3 days ago”, so the API is rather correct. Maybe the timestamp shown on the item page is incorrect, or that the url was re-submitted?
I noticed that when one of my posts is resubmitted (via second-chance pool) it seems to appear with the time of the resubmit and not the time I posted it originally. I observed this on the website, I never checked the API and maybe this is unrelated to the original question from above. It may even be intentional but probably not many posters know about it.