Command block cannot do /Time set 0

What I expected to happen was...:
The command block was going to set the time to 0

What actually happened was...
It said: Unknown Command: Type /help for a list of commands.

Steps to Reproduce:
1. in a command block put Time set 0 in "Input"
2 Activate a redstone charge to the command block.
3 Look at the command block in "Output"