The problem here is that the phone company has an incorrect time setting on their end, which is being automatically broadcast as a time signal along with the caller id information, causing the phone to constantly be out of sync.
To correct this, you'll need to disable the auto time set (manual mode), set the time once more, and then the setting should stick.
Grab a handset and key in Menu # 2260 (Or Menu#226, up/down to MANUAL)
Then, Menu#101 to re-enter the date and time.
Note: you only have to do this once, it will apply to the entire system, it does not have to be done on the base and each handset individually.
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