"ROI of 333days" -
There was never a ROI of 333 days. Your calculations are totally wrong.
Not my calculation, it is the calc from ONLYfree!
...and I know it is only a game.
You can be online once in 40 hours to collect all production.
Then you should sell an "autocollector" (...as an item?! ...with some levels?) which expand this "40 hours" time.
The game-idea is great. Good luck!