title: Timestamp accuracy in Firebase Analytics
body: <p>We've just started using Firebase Analytics and have exported all the events to BigQuery. While processing the "app_remove" event we noticed an odd thing. Sometimes our servers record activity from the app after the timestamp of the app_remove event (i.e. event_dim.timestamp_micros). </p>
  
  <p>While running, the app periodically contacts our servers and we then record the UTC time of that request. Sometimes the latest activity time is higher than the timestamp of app_remove event. The largest time difference we've noticed is 12h 23m 17s. </p>
  
  <p>Each app instance gets a unique certificate that it uses when authenticating with servers so if an uninstall completes it's impossible to record any new calls for that app instance, even if you reinstall. After reinstall a new certificate is issued and the activity time would be recorded on a different row in the db.</p>
  
  <p>How could this occur? Are the timestamps of app_remove set by the client so it could be caused an incorrect clock on the user's phone? How else could it occur? </p>