MQTT timing issue

1

I have built an ambient light sensor that delivers the light level (lux) to Home Assistant via an MQTT message every 5 minutes. On the face of it, it works well.

sensor:
  - name: "Hall ambient light"
    unique_id: 123456789
    state_topic: "home/hall/ambient"
    value_template: '{{ value_json.illuminance | int }}'
    qos: 0
    unit_of_measurement: 'lux'

I have an automation that is triggered by the arrival of this MQTT message and switches a light on/off depending on the light level. This also appears to work.

- id: '1723227061809'
  alias: Hall Ambient Light
  description: Turns hall table lamp on/off depending on amount of ambient light
  trigger:
  - platform: mqtt
    topic: home/hall/ambient
  - platform: time
    at: 06:30:00
  - platform: mqtt
    topic: home/hall/ambient
  condition:
  - condition: time
    after: 06:29:00
    before: '22:00:00'
  action:
  - if:
    - condition: numeric_state
      entity_id: sensor.ambient_light
      below: 25
    then:
    - action: homeassistant.turn_on
      metadata: {}
      data: {}
      target:
        entity_id: switch.hall_table_lamp
    else:
    - action: homeassistant.turn_off
      metadata: {}
      data: {}
      target:
        entity_id: switch.hall_table_lamp
  mode: single

However, I have discovered that the automation is not responding to the lux value in the current message, but instead it is reading the stored lux value received 5 minutes earlier.
Can anyone let me know how to get the automation to read the current lux value held within the MQTT message? Thank you.