I wrote an experimental add-on that can make screenshots of any dashboard or page in the HA UI. home-assistant-addons/puppet at main · balloob/home-assistant-addons · GitHub
It’s around ~10s cold start on a HA Green (has to launch Chrome!). Same page subsequent screenshots are 0.7s, while different pages are 1.5s. Browser will be automatically closed after 30s to release memory.