Start by creating a light schedule using the Home Assistant Times of Day helper as shown in light schedule, then create a basic 'turn on' automaiton using the GUI or yaml:
alias: Aquarium Light - Turn On
description: ''
trigger:
- platform: state
entity_id:
- binary_sensor.aquarium_light_schedule
to: 'on'
condition: []
action:
- service: light.turn_on
data: {}
target:
device_id: <<< put your device uuid or name here >>>
mode: single
Then add a 'turn off' automation:
alias: Aquarium Light - Turn Off
description: ''
trigger:
- platform: state
entity_id:
- binary_sensor.aquarium_light_schedule
to: 'off'
condition: []
action:
- service: light.turn_off
data: {}
target:
device_id: <<< put your device uuid or name here >>>
mode: single
Note that both automations refer to the Light Schedule helper.