a.yaml

input_boolean:
  uf_lamp:

input_number:
  on_seconds:
    min: 0
    max: 10000000000
    step: 1
    mode: box

  off_seconds:
    min: 0
    max: 10000000000
    step: 1
    mode: box

  timestamp:
    min: 0
    max: 10000000000
    step: 1
    mode: box

switch:
  - platform: template
    switches:
      uf_lamp:
        value_template: "{{ is_state('input_boolean.uf_lamp', 'on') }}"
        turn_on:
          service: input_boolean.turn_on
          entity_id: input_boolean.uf_lamp
        turn_off:
          service: input_boolean.turn_off
          entity_id: input_boolean.uf_lamp

sensor:
  - platform: history_stats
    name: Switch on
    entity_id: switch.uf_lamp
    state: 'on'
    type: time
    start: '{{ 0 }}'
    end: '{{ now() }}'

  - platform: history_stats
    name: Switch off
    entity_id: switch.uf_lamp
    state: 'off'
    type: time
    start: '{{ 0 }}'
    end: '{{ now() }}'

automation:
  - trigger:
      platform: state
      entity_id: switch.uf_lamp
      to: 'on'
    action:
      - service: input_number.set_value
        data_template:
          entity_id: input_number.off_seconds
          value: "{{ states('input_number.off_seconds') | float + ((as_timestamp(now()) - (states('input_number.timestamp')) | float)) }}"
      - service: input_number.set_value
        data_template:
          entity_id: input_number.timestamp
          value: "{{ as_timestamp(now()) }}"

  - trigger:
      platform: state
      entity_id: switch.uf_lamp
      to: 'off'
    action:
      - service: input_number.set_value
        data_template:
          entity_id: input_number.on_seconds
          value: "{{ states('input_number.on_seconds') | float + ((as_timestamp(now()) - (states('input_number.timestamp')) | float)) }}"
      - service: input_number.set_value
        data_template:
          entity_id: input_number.timestamp
          value: "{{ as_timestamp(now()) }}"