Open random page of kyselo right from unix terminal
Run command below in your unix terminal
$ firefox https://kyselo.eu/all?since=$(TZ=Europe/Prague date -d @$(shuf -i $(($(TZ=Europe/Prague date -d '2020-07-13T00:35:49' +"%s")))-$(date +"%s") -n 1) +"%Y-%m-%dT%H%%3A%M%%3A%S")
2020-07-13T00:35:49 is the date of first post in server time, replace 'firefox' with your browser command if you have different browser installed.
Edit: Added correct timezome matching to kyselo to command line, found by examining date of some posts and choosing correct timezone matching the site location.
Edit2: Shortened command a bit by inlining some variables used before.