earth_hour.yaml

- alias: Earth hour starts
  trigger:
    platform: time
    after: "20:30:00"
  condition:
    condition: time
    weekday:
      - sat
  action:
    service: light.turn_off
    entity_id: group.all_lights
    
- alias: Earth hour ends
  trigger:
    platform: time
    after: "21:30:00"
  condition:
    condition: time
    weekday:
      - sat
  action:
    service: light.turn_on
    entity_id: group.all_lights