Aha, well it's certainly been a learning curve for me!

I found the public MIT lectures on "retroactive data structures" (by Erik Demaine) very helpful to clarify the mental model and properties of temporal databases. Point-in-time bitemporal queries are fairly simple compared to the kinds of things some organisations use data warehouses for (e.g. temporal range queries across N dimensions), but surprisingly few teams think about representing time so clearly within their transactional OLTP/HTAP systems, so even point-in-time queries seem more novel than they really should.

Everything is moving in the right direction though as immutable data becomes the default.