potato's could be rare wild mobs(no spawners)and when bitten by an npc potato theres a small chance (10 percent maybe?) that you will be turned into a were potato dosnt nead day and night just at random times
So, you want a wearoffpotato?
...Sorry, terrible pun :P
Cool idea, but we should never turn into a potato while being a zombie and the were potato should wear off.