Very interesting stuff. One of the fun bits of being a time-nut is that there are somewhere around 15 orders of magnitude available to play with. Getting clocks synced to within a few milliseconds is child's play, even for an amateur with $15 of hardware. Getting clocks synced within a few dozen microseconds is possible with GPS and some minor effort. Getting clocks synced within a few nanoseconds requires a lot more effort. I have never attempted anything below the ns range, but this process seems to produce clocks in sync within hundreds of attoseconds! This is within around 10^-16 seconds. Quite amazing if you ask me.