Their alternative to NTP (and, it should be noted, NTP is never once mentioned in their paper), TrueTime API is actually pretty impressive. They are able to ma

Their alternative to NTP (and, it should be noted, NTP is never once mentioned in their paper), TrueTime API is actually pretty impressive. They are able to maintain <10ms latency 99.9% of the time across data centers all over the world. That's not something you can easily do with NTP over the internet. Placing Stratum-0 receivers (and, in fact, Stratum 0 devices) in their data centers isn't unheard of, but that alone won't get you the kind of global-temporal-synchronization that Google is able to achieve with TrueTime API. I'm looking very forward to the paper on that protocol/system which will hopefully be forthcoming - They tease it with this: "This section describes the TrueTime API and sketches its implementation. We leave most of the details for another paper: our goal is to demonstrate the power of having such an API."