Dunno... Italians keep it until they eat it all. THAT usually doesn’t take more than a few weeks!
Seriously, about a year. Just be sure no parts are sticking out of the oil, not even a sliver of garlic or a basil leaf. The oil should go rancid before the submerged eggplant goes bad. AND you’ll KNOW that!
More important, what I did not see or hear: Hillary and her "Rope A Mope" media strategy. Two observations about that:
1. By having the emphasis on the rope, the media could avoid having to talk about how thin the crowds were.