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Build a simple Timer ON OFF by יובל מג'הז
On the configurations.yaml or external file you have setup
 
1.add sensor Time & Date to the sensor: 
  https://www.home-assistant.io/components/sensor.time_date/
sensor:
 - platform: time_date
   display_options:
    - 'time'       #only time
    - 'date'       #only date
    - 'date_time'  #format date first and time
    - 'time_date'  #format time first and date
    - 'time_utc'   #internet time
 
2. add an INPUT_BOOLEAN
   exemple: 
           input_boolean:
            turbo_boiler_timer:
            initial: off
 
3. add 2 variables to the INPUT_DATETIME
    input_datetime:
     boiler_start:
     name: שעת התחלה
     initial: 00:00
     has_date: false
     has_time: true
    boiler_end:
     name: שעת סיום
     initial: 00:00
     has_date: false
     has_time: true
 
4. Configure 2 automations to check between the set point to the current hours
   automations.yaml
#############################################
# boiler on  clock                                                   
#############################################
- id: Turbo_Boiler_Timer_Start
  alias: "Turbo Boiler Timer Start"
  initial_state: 'on'
  trigger:
    platform: template
    value_template: "{{ states('sensor.time') == (states.input_datetime.boiler_start.attributes.timestamp | int | timestamp_custom('%H:%M', False)) }}"
  condition:
    condition: state
    entity_id: input_boolean.turbo_boiler_timer
    state: 'on'
  action:
    - service: switch.turn_on
      entity_id: switch.turbo_boiler
#############################################
# boiler off  clock
#############################################
- id: Turbo_Boiler_Timer_Stop
  alias: "Turbo Boiler Timer Stop"
  initial_state: 'on'
  trigger:
    platform: template
    value_template: "{{ states('sensor.time') == (states.input_datetime.boiler_end.attributes.timestamp | int | timestamp_custom('%H:%M', False)) }}"
  condition:
    condition: state
    entity_id: input_boolean.turbo_boiler_timer
    state: 'on'
  action:
    - service: switch.turn_off
      entity_id: switch.turbo_boiler
    - delay: 0:00:03
    - service: input_boolean.turn_off
      entity_id: input_boolean.turbo_boiler_timer
 
5. restart HA
 
6. configure the ui-lovelace.yaml
   - id: ea21d03d4002483ea4ff39cee45021ad  # Automatically created id
     type: entities
     title: טיימר - מאיץ חימום מים
     show_header_toggle: false
     entities:
      - input_boolean.turbo_boiler_timer
      - input_datetime.boiler_start
      - input_datetime.boiler_end