Seems like it would either need to be append only or have some kind of snapshot isolation

Google Developed Spanner which is a globally distributed database that uses atomic clocks to keep things synchronized: https://static.googleusercontent.com/media/research.google.c...

I think the Chandy-Lamport snapshot algorithm tries to do something like this for all distributed systems (in their model, and it tries to get any consistent snapshot, not allowing you to specify the "time"); not sure if it's actually useful IRL though