Check for last transitioned state in waze sensor (e.g. don't run if it was unknown)

This automation runs every time after a reboot (not meant to), i guess the sensor goes from something to a value below 5. But what that value is i can’t see or figure out, i’m hoping it’s unknown.

Now I could use the current condition and check for uptime, but it seems more appropriate to check the sensor for a unknown condition (so i know it transitioned from unknown to a known value ?

I couldn’t find the syntax of how to check for the last transitioned state. I also couldn’t see it in the history_stats (maybe it doesn’t ever have a unknown state?)

Any help would be appreciated here.

alias: Announce when car is x amount of minutes away from home (arriving)
description: test
  - platform: numeric_state
    entity_id: sensor.waze_travel_time_2
    attribute: duration
    below: "5"
  - condition: template
    value_template: >-
      {{ ( as_timestamp(now()) - as_timestamp(states('sensor.uptime'))) // 60 >
      1 }}
  - service: notify.alexa_media_everywhere
        type: announce
        method: all
      message: >-
        "Car is expected to arrive home in {{
        state_attr('sensor.waze_travel_time_2','duration')|round(1) }} minutes" 
mode: single