Broadsword Online Games had to revert time on — and, in fact, temporarily shut down — the Yamato shard today:

We have experienced some issues with the backup on Yamato hanging up causing issues and not allowing players to log in. To fix this we are having to do a 7.5 hour revert on Yamato. We have currently taking it down and are working to get it back up. We are sorry for the inconvience and will get it back up as soon as possible.

This is actually a fairly significant issue, given the still-quite-large player base that Ultima Online enjoys in Japan.