Voice Help

Ok so a little background before I get started. I was fairly active in the mycroft community forum and developed some skills for that product. With it’s demise I have been watching carefully on the two branches that have been continuing their development with interest. Now that HA has entered the Year of the Voice I am very interested in how this plays out. I thought I would begin by understanding the “skills” and how intents / sentences are developed. I have created a “skill” that is working but I want to make it more generic and I am struggling figuring this out. My plan is to develop a “timer” skill/intent that will set a timer that I can use for different functions. At this point it is working but I want to have the timer value set based on a keyword (seconds, minutes, hours). I can’t get this to work and hoping someone else has some idea on this. Here is my “skill” as it is working…

# /homeassistant/custom_sentences/en/timer.yaml
# Timer Voice Control Created 2023-07-03
# Create a timer helper calleed "voice_timer"
# Changed file name to SetTimer.yaml
language: "en"
intents:
  SetTimer:
    data:
      - sentences:
        - "(set|change) [the|a] timer for {timer_value} seconds"
#        - "(set|change) [the|a] timer for {timer_value} {duration}"
        
lists:
  timer_value:
  # in Seconds
    range:
      from: 0
      to: 60
#  duration:
#    values:
#      - in: "seconds"
#        out: "00:00:" + {{ timer_value }}
#      - in: "minutes"
#        out: "00:" + {{ timer_value }} + ":00"
#      - in: "hours"
#        out: {{ timer_value }} + ":00:00"
# /homeassistant/custom_intents/intents.yaml
# Timer Voice Control Created 2023-07-03
  SetTimer:
    action:
      service: "timer.start"
      data:
        duration: "{{ timer_value }}"
      target:
        entity_id: timer.voice_timer
    speech:
      text: "The Timer has been set with a value of {{ timer_value }}"

My plan was that I would use duration as a string (hour, minute, seconds) to set the timer but this does not work as I expected.
Any Ideas??