I was unable to find much information about this, but see the previous commit and Brave Leo said
> Yes, it's generally acceptable to use interleaved mode with a public NTP (Network Time Protocol) server, as long as you comply with the server's usage policies. This mode allows for time synchronization while also providing a fallback if the primary time source fails. However, keep in mind that public NTP servers are often subject to heavy traffic, so they may not provide the most accurate or timely synchronization.
The ISP should be closest server to sync to and Cloudflare is anycast with
potentially lower stratum than the other nts servers. 'nts' implies 'require'
and 'trust' already and other servers get picked over lower stratum although
higher distance.
I hope these are wider defaults than just Debian and allow me to not
conflit with package manager, but regardless having a separate
sources.d/ looks like a good idea for being able to `chronyc reload sources`
Aminda Suomalainen