Is the free tier actually free, or a trial?
It's free for as long as you would like to use it. Up to 20 devices, no countdown. If you run a small environment or you just want to model your own network, you can stay on free as long as you'd like.
The free plan provides an indefinite lifetime, there’s no timer that will switch you over to a paid plan. You can get access to Palpabl through the pricing page and selecting the free plan.