This spews out this exception when used in the console, and crashes the client when used in-game.

Full stack trace: https://gist.github.com/58a56b49c48e73f24ddacdfed2393ccb

Which exact command? Does it work without FastCraft?

I said, /timedmessage list. That's the actual command. And I don't see how FastCraft would be causing an issue here since it's related to ChatComponentTranslation, and it crashes the client.

That wasn't clear. You didn't copy the command in the message body, and dechiphering all wrapped around subject isn't the most pleasing task.
Thanks for the report.