I came across this article: https://www.bbc.com/news/technology-47198426
This seems to be an interesting test and I wonder if there is any pool DNS server located inside Russia?
If not, resolving “ru.pool.ntp.org” would be impossible for the time of the test, which therefore could lead to interesting failures - i.e. rebooting of a device without a built-in RTC…
Even if the zone can’t get updated from outside russia, the at-the-time working zone should be fine enough, but (of course) only, if DNS resolution is still working.