There is already NaiveDateTime::from_timestamp_millis, which uses some non-trivial logic to convert properly to seconds and nanoseconds when dealing with pre-1970 timestamps.

When instantiating one from a timestamp in microseconds (which we have seen in the wild from some of our customers), it's necessary to duplicate that logic; see e.g. MaterializeInc/materialize#16609 .

It would be really nice if Chrono had a from_timestamp_micros feature for this case.