I believe the algo is somewhat timezone based, too.

Very common for ppl to be served Chinese or asian influencer content after 12pm (EST). So common, in fact, most of the western users begin posting "whelp, time to go to bed!"

The majority of the content feels regional, though.

I've never used tiktok... Do you mean 12AM (midnight)? Or are people commonly in the habit of mid-afternoon naps?

12PM is Noon. Did you mean Midnight?