How to size green bar in Thruk?

Hope I’m in asking in the right place.

We’re running Thruk as our front end for monitoring, Naemon backend with various Nagious plugins.
Some of these plugins produce output that sizes the green bar in the screen (eg disk space).

Now we’re also monitoring our Let’s Encrypt certificates. I note that the default just makes the entire bar green.

We’ve been having problems with some certificates not renewing automatically.

What (and how) do I have to change (it) so that the green bar shows the time left for the certificate?

does the check return performance data? Afaik check_http -C did not return performance data for a long time.