Flux Config From Lovelace

Hi, I just found about Flux in Homeassisant.
I’m trying it, see if it works for my lights, instead of installing another HACS integration I don´t understand yet.

Anyway, Flux is not configurable on Lovelace, only directly on yaml.
So I thought I could create a card to config my lights from it. I know I still have to restart after any change.

Nut the problem is that I could not figureit out how to get a helper value directly in configuration.yaml. I get a config error.

I created a helper to specify the start_time config and tried to get the value from the helper. See de code below. Is it possible to user the jinx on configuration.yaml ?

- platform: flux
  lights:
    - light.yuri_fishtank_panel
  name: Fishtank Panel
  start_time: {{ states('input_datetime.start_time') | timestamp_custom ('%H:%M') }}
  stop_time: "23:00"
  start_colortemp: 4000
  sunset_colortemp: 3000
  stop_colortemp: 1900
    #brightness: 200
    #disable_brightness_adjust: true
  mode: rgb
  transition: 30
  interval: 60