Great list! Just double-checked the CAT timekeeping requirements [1] and the requirement is NIST sync. So a subset of all UTC.

You don’t need to actually sync to NIST. I think most people PTP/PPS to a GPS-connected Grandmaster with high quality crystals.

But one must report deviations from NIST time, so CAT Reporters must track it.

I think you are right — if there is no NIST time signal then there is no properly auditable trading and thus no trading. MFID has similar stuff but I am unfamiliar.

One of my favorite nerd possessions is my hand-signed letter from Judah Levine with my NIST Authenticated NTP key.

[1] https://www.finra.org/rules-guidance/rulebooks/finra-rules/6...