/setidletimeout does not work

/setidletimeout for Realms it not working

What I expected to happen was...:
I could change or stop the kicking for being idle.

What actually happened was...:
The Minecraft Chat responded with the following error: You do not have permission to use this command. (I am the owner of the Realm).

Steps to Reproduce:
1. Open Minecraft
2. Set up Realm
3. Type in chat: /setidletimeout (time)