How much is the time off? Does the time always reset to some constant value?
If the time is constantly incorrect thus needing to be reset then there is a problem with either: 1) some internal power source that keeps the time, 2) maybe the TV is losing power via a problem power adapter or even the electrical outlet, or 3) the TV is getting the time and date via another source. - check the menu settings for any such options.
I found some specifications that stated "no battery".
During the day, unplug the TV for a few minutes and then other increasingly longer amounts of time. Turn the TV on again and see if the time needs to be reset.
May not require resetting until after some specific elasped time. Then you will know that it...