Hi there,
So from the Quoted Question, to google AI , apparently So, However not really related to this topic.
I won’t spoil the journey of discovery for you , but snip this to You.
Yes, it is possible to automatically synchronize time using OpenThread with SNTP over IPv6, but with important caveats. While OpenThread has its own native time synchronization feature for internal network use, it can be configured to use an external SNTP server, including one accessible via IPv6. However, the OpenThread time sync service is separate from SNTP, and it is the responsibility of the device acting as the SNTP server to provide IPv6 connectivity to its clients.
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However I think it will be an issue here:
" For a device in an OpenThread network to synchronize with an external SNTP server, it must have an IPv6 route to that server. This means the Thread network must have a connection to the external world, either through a Border Router or a device that acts as an SNTP server with an IPv6 address. "
GL 
PJ 