Track Reboot Time

I use the automation below to inform me when HA has stopped and started.
It SEEMS TO ME that sometimes it takes for ever and other times just a minute or so.
Is there a way to track (calculate) the time that it took from start to stop and tell me in my notification.
Thank you for the help.

#########################################################
#                   HOME ASSISTANT START                #
#########################################################
  - alias: Home Assistant Started
    trigger:
      platform: homeassistant
      event: start
    action:
      - service: notify.telegram_carlton
        data:
          title: "Home Assistant Started"
          message: "Home Assistant Has Started as of {{ now().strftime('%A, %B %d, %Y %I:%M:%S %p') }}"
      - delay:
          minutes: 1
      - service: homeassistant.turn_on
        entity_id: automation.addon_update_available
#########################################################
#                   HOME ASSISTANT STOP                 #
#########################################################
  - alias: Home Assistant Stopped
    trigger:
      platform: homeassistant
      event: shutdown
    action:
      - service: notify.telegram_carlton
        data:
          title: "Home Assistant Stopped"
          message: "Home Assistant Has Stopped as of {{ now().strftime('%A, %B %d, %Y %I:%M:%S %p') }}"
####################################################
#            END OF CONFIGURATION FILE             #
####################################################

Set an input_datetime to now() in your stopped automation actions.

Subtract that datetime from now() in your started automation. Store the result in another input_datetime or input_text (or even the same input_datetime).

Thanks, worked perfectly.