Thanks @chrishamm. Reading your response made me realize that I not only mistyped "SBC" but also that I was backwards about it. My system is NOT running in SBC mode, it's stand-alone. So thanks for answering that version of the question.
I'm restating your "never supported NPT" comment to see if I understand the implications for a machine running in stand-alone mode:
The stand-along RRF will not "know" the time until a client connects. This means all log entries will have a timestamp based on the machine's uptime (time since boot).
If/When a client connects, if that client is DWC, then DWC will set RRF's date-time.
If a client other than DWC connects, and it connects using rr_connect with the time option, then RRF will update with the time from the client.
This explains a lot of unexplained macro errors I've observed over the past three years. And I can see now that I'll need to rewrite all the macros to not use state.time for measuring duration. I'll convert them all over to using state.upTime rather than state.time.
I think I'll also look into making an Rpi pico that powers up with my system and that does the rr_conenct function.