The RTC may not be set yet, may have been reset, or may have drifted significantly if the device time hasn't been updated in a long time. Using the the last_time_change file to determine if the time is known to be accurate and only display the clock when that is the case. Bug: 27802041 Change-Id: I845cf9c74fcb4009504f1bab853e04146fa19e1d