I wonder what kind of accuracy could be had with a cheapie USB GPS receiver. I wouldn't use that anywhere I had Internet connectivity, but in a disconnected location I wonder if it would get within a few ms of GPS time. I have an old USB GPS that shows up as a serial device (FTDI, or more likely a counterfeit) that I used back in my wardriving days, and later for moving map navigation on a laptop on road trips (as a dedicated navigator/passenger). It might be fun to dig it up and try it out.

Since I know Jeff frequents HN I'll go meta for a second and say that I noticed the Neatpatch cable management in the rack. I've been a fan of Neatpatch for a good long time. I don't use them in racks there there will be much churn, but they're mighty nice in locations that get wired once and only touched again when switches get replaced. It really makes a rack look-- erm-- nest.