There were times when we were traveling when it just wasn't convenient, so I used the jarred baby food, and I think for the most part it's fine. But Presley definitely prefers the fresh food. I would say two or three days. And also, pour out from the jar, or whatever serving piece the food is in, small amounts as you need them, but avoid dipping the spoon from the baby's mouth into a big bowl of food and then saving that. Also, you can freeze baby food if you make a big batch, in ziplock bags.
Some people even pour the pureed vegetables etc.
Be careful if you use a microwave to reheat, because sometimes there are hot spots. Make sure you really stir it well and then taste it yourself. I've tried several different brands of rice cereal and brown rice cereal, and organic brown rice cereal, and haven't really noticed a difference in anything but the price. Just make sure you like the taste and smell. Presley is primarily getting most of his nutrition now from formula.