I have created a materialized view (MV) and a corresponding NATS sink to publish average temperature data every 3 minutes. However, I'm receiving updates on the temperature.avg.3min topic every 3 to 5 seconds instead of every 3 minutes. Here's the SQL for the MV and sink:

CREATE MATERIALIZED VIEW IF NOT EXISTS avg_temp_3min AS
  SELECT temp_demo.window_end AS window_end,
        temp_demo.device_id AS device_id,
        AVG(temp_demo.temperature) AS avg_tmp
  FROM (
      SELECT device_id, window_end, AVG(temperature) AS temperature
      FROM TUMBLE(
          temperature_src,
          ts,
          INTERVAL '3' MINUTE
      ) GROUP BY device_id, window_end ORDER BY window_end
  ) AS temp_demo
GROUP BY temp_demo.device_id, temp_demo.window_end;

CREATE SINK IF NOT EXISTS temp_avg_sink_3min FROM avg_temp_3min
WITH (
  connector='nats',
  server_url='nats-server:4222',
  subject='temperature.avg.3min',
  type = 'append-only',
  force_append_only = 'true',
  connect_mode='plain'
);

I expected to receive updates only when the 3-minute window ends, but it seems to be sending updates more frequently. How can I adjust the setup to only send updates every 3 minutes as intended?