Long story short:
We didn't even have a roster - so effectively 365 days on unless the aircraft was away with the other 2 pilots or in maintenance.
Owner flights were generally notified at least a day in advance (don't recall it ever being less than 24 hours to be fair) but charters could be short as 2-3 hours.
Pretty horrific and fortunately that 'operation' is now behind me where it belongs.