Handling feed dates that are inaccurate

[ChrisHardie]

I'm trying to work around some of the feeds I ingest having inaccurate dates - shifted by a day in the past or future, wrong time zone, etc. My goal is to have newly published posts from a feed use a post published date of when the feed was read and the item appeared in it for the first time.

When I tried to do this by filtering on syndicated_item_published and having it return the current timestamp, I found that it was applying not only to new posts, but to every existing post in the database for that feed ingestion session, and subsequently triggering new revisions to those existing posts - not good.

I'm hoping to avoid hooking on post_syndicated_item and retroactively updating a post that has been published.

Can you recommend a best practice here? Or would a new filter be helpful?