[T3OU-736]

This may be a naive question: is using a NIC with PTP (nee IEEE-1588) an option for a time source?

Or am I thinking of two completely diverse time source paths, at utterly different HW stacks?

[bcrl]

As soon as you're talking about going outside of the CPU core you're in the territory of slow, and going off chip over PCIe is very slow (hundreds of nanoseconds). That's why many apps continue to make heavy use of rdtsc with all of its quirks and foibles.