Done some more testing ... verified (contrary to my now-deleted post) that 12h long running sessions indeed do expire, leaving rclone with recurring messages like 2023/02/19 00:00:23 DEBUG : pacer: low level retry 1/2 (error ExpiredToken: The provided token has expired.
It is possible to then kill the process, get new temp creds for another 12 hours, manually import them into the environment and restart rclone. That's not a viable solution
If (see --s3-profile failing when explicit s3 endpoint is present - #4 by robinpc) the --s3-profile option worked with endpoints, which it appears not to, this problem might be easily resolved, because apparently the use of a named profile from the CLI also caches and automatically renews the temporary credentials (per this longish post, search for "cache")
So maybe, just maybe, getting s3-endpoints working with --s3-profile will solve both the "need endpoints" and the "need refreshable creds" problem.
Any progress?