I do something similar. I use the built in light brightness transition property which does the smoothest transition. Here’s an example of my 3 year old daughter’s wakeup light where the light will be at full brightness (255) in 900 seconds:
And this is how my flow looks like. I’ve tried it several ways and for some reason this is the way it works. I turn on the light at 1 brightness, delay 5s, and do the transition. If I connect the delay on the top turn on node, it doesn’t work:
