This message appears because the device time is not corresponding with what the server expects. Apple devices can reset back to 1970 if left to un-charge completely, so please check the device time and change it if necessary to clear up the message. To change the device's time/date, please following the below instructions.
STEP #1: Go into the device's settings and select Date & Time.
STEP #2: Select Set Date & Time.
STEP #3: Tap the date shown and change to today's date.