40 minute update time is of dubious accuracy.

[JeremyRand]

dot-bit/index.md states:

Dot-Bit's phonebook updates within 40 minutes on average with default settings.

AFAICT this is based on the 10-minute target block time, plus NMControl's 30-minute cache, right? ncdns's caching behavior is different from NMControl; there's not necessarily any reason to wait for 1 block with a full node; it's probably not safe to only wait for 1 block with an SPV node; and there are also probably caching behaviors by Unbound and the OS that we need to take into account.