Clock settings are disabled from Time & Date Settings [closed]
I realize that this is an old issue, but given that I experienced the same problem, and that this question comes up high in Google, I figured I'd put a response in.
In Ubuntu 13.10, I had the same issue, and I solved it by entering the following command in the terminal:
killall unity-panel-service
This immediately reset the panel, and displayed the clock.
Obviously, I was running Unity when I experienced this issue.
I found this answer at Upgraded to 13.10 now clock settings are all disabled and clock does not display