code: private void invalidateSync() {
          Log.d("AndroidClockSync", "Starting sync...");
          new Thread() {
              @Override
              public void run() {
                  SntpClient client = new SntpClient();
                  ExponentialBackoff exponentialBackoff = new ExponentialBackoff();
                  while (!client.requestTime(serverHost, 10000)) {
                      exponentialBackoff.onFailure();
                      try {
                          Thread.sleep(exponentialBackoff.exponentialWait());
                      } catch (InterruptedException e) {
                          e.printStackTrace();
                      }
                  }
                  syncDelta = client.getClockOffset();
                  preference.edit().putLong("delta", syncDelta).commit();
                  Log.d("AndroidClockSync", "Synced. Time delta: " + syncDelta + " ms");
              }
          }.start();
      }
docs: TODO: Better invalidation