Command block

[xoft]

Judging from the source code, you need to use the commands without the leading slash ("time") and you need to specify the world (for now), because the commands are executed as if in the server console. That means that the command itself has no knowledge of the world in which it is executing. I believe the proper format for the console command is either "time day <worldname>" or "time set day <worldname>", try those.