Very interesting idea, of course it's only useful when the server restarts (as mentioned), so time doesn't pass by while there are no companies.
I however disagree that AFK players would count as offline, I can only see this being useful when the server is empty, and only right after a restart, because if there's like a few years left till an automatic restart happens, it's no good if it's paused.. what if people are waiting to start a company after the server restarted.
Afaik, OpenTTD doesn't have a setting for this, but if should be fairly easy to do with a script, which is already included in xShunter.