Template: measurement duration worktime from local calender

Hi,
i need help with a calendar action. i have two entries in my calendar.
Work begin and work end.
And now i would like to measure the time between this entries and writes a third entry with the measured duration in hours. If hours are about 8 hours, ist should be red entry otherwise without special color. How can i do this?

I try the automation:

description: ""
trigger:
  - platform: webhook
    allowed_methods:
      - POST
      - PUT
      - HEAD
      - GET
    local_only: false
    webhook_id: mysecretID
    id: Arbeitsanfang
condition:
  - condition: template
    value_template: "{{ trigger.data.user_name == 'myusername' }}"
action:
  - service: notify.mobile_app_iphone14
    metadata: {}
    data:
      message: "message: '{{ trigger.data.user_name }}'"
      title: Webhook ist da
      data:
        message: "{{ trigger.data.user_name }}"
  - choose:
      - conditions:
          - condition: template
            value_template: "{{ trigger.data.command == '/start' }}"
        sequence:
          - service: calendar.create_event
            metadata: {}
            data:
              summary: Arbeitsbegin
              description: Los gehts
              location: Firma
              start_date_time: "{{ now() }}"
              end_date_time: "{{ now() + timedelta(minutes=1) }}"
            target:
              entity_id: calendar.arbeit
      - conditions:
          - condition: template
            value_template: "{{ trigger.data.command == '/ende' }}"
        sequence:
          - service: calendar.create_event
            metadata: {}
            data:
              summary: Arbeitsende
              description: Für heute reicht es
              location: Firma
              start_date_time: "{{ now() }}"
              end_date_time: "{{ now() + timedelta(minutes=1) }}"
            target:
              entity_id: calendar.arbeit
          - service: calendar.get_events
            target:
              entity_id:
                - calendar.arbeit
            data:
              start_date_time: "{{ now() }}"
              end_date_time: "{{ now() }}"
            response_variable: liste
          - service: calendar.create_event
            metadata: {}
            data:
              summary: Zeit
              description: liste
              location: Arbeitszeit
              start_date: "2024-02-16"
              end_date: "2024-02-16"
              duration: 24
            target:
              entity_id: calendar.arbeit
          - service: notify.telegram_notify_user
            metadata: {}
            data:
              message: >-
                {{ (liste.events | selectattr('start', 'eq',
                (now()+timedelta(days=1)).date()|string ) | first).summary }}
          - service: ""
            data: {}
mode: single
type or paste code here

i get two webhooks which enter the entry for work beginning and end… that works…

But the measurement is thy problem…

thanks for help…