Disable system time change

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You can have an administrator account with a secure password so users can't use it. You should never use administrator account for day-to-day usage (although i am a hypocrite but i am the only user)
Every user should be in a custom "groups". Set this group up to give them any permission you want but lock the time change out. Make sure it's the only group they are in. Regular users should NEVER have admin privelages. They can mess up stuff on accident and not even know they did it.

Actually, the system is not created by us but by a third party team and their requirements is to use an Admin account, so we have no choice.. ^_^