Date and time unchangeable
YOU might have a problem with permissions..


One is to restore system level permissions using the Disk Utility.
and use  this for Home Folder to restore them do following.:



  
  Restart OS X and hold down the Command and R keys.
  You will boot into the Repair Utilities screen. On top, in the Menu Bar click the Utilities item then select Terminal.
  In the Terminal window, type “resetpassword” (without the quotes) and hit Return.
  The Password reset utility launches, but you’re not going to reset the password. Instead, click on the icon for your Mac’s hard drive
  at the top. From the drop-down below it, select the user account where
  you are having issues.
  At the bottom of the window, you’ll see an area labeled ‘Reset Home Directory Permissions and ACLs’. Click the Reset button there.
  
  
  The reset process takes a couple of minutes.