DIAGNOSIS The clock is network-synced. Flashing means it lost connection or failed its time sync. A consistent offset is a software bug.
FIX Ensure the Dot has a stable Wi-Fi connection. Say, "Alexa, what time is it?" to force a sync. In the Alexa app, go to Device Settings > your Echo > Clock & Display > Time Zone and verify it's correct.
IF THAT DIDN'T WORK Perform a factory reset (hold Action button 35+ seconds). During setup, the app will explicitly ask for time zone confirmation. Do not skip this.
HEADS UP The clock display brightness is tied to the ambient light sensor. If the sensor is blocked, the clock may appear off or too dim, not incorrect.