I'm posting this response simply to add to the information here on the configuration of the acme plugin to successfully create/renew a Let'sEncrypt certificate. I had quite a struggle to get it to work and also got a timeout error message.
It seems essential that port 80 is open for the pfSense web interface. Under "System / Advanced / Admin Access" the WebGUI redirect" tickbox must not be ticked, to allow port 80 to be redirected to port 443. If this is ticked, port 80 does not respond and the certbot script to fails.
Under "Services / Acme / Certificate options: Edit" it's easy to miss the small little "+" for RootFolder under Domain SAN list.
Here's the spot!
Domain SAN list small plus
Ensure that the directory is specified.
Lastly, I have created a firewall rule that allows port 80 access to "this firewall" in the WAN rules. I did this before I discovered point 1 above, so it may not be required, but I'm not going to delete my cert now to test it again :-)
Hope that helps future finders of this thread.