Up to Four Days
After a certain period in the fridge, food will start to grow mold or bacteria that can be harmful to your health. According to Katherine Zeratsky, a nutritionist at the Mayo Clinic, you can keep leftovers in the fridge for up to four days. Leftovers are defined as food that has been prepared in any way, whether cooked or cut.
Use your Judgment
You may want to use the zucchini before four days are up, depending on what you use them for. If they are to be cooked into a quiche, for example, their texture and color does not matter as much. If you want to use the zucchini raw in a salad, though, keep an eye on it to make sure it is not going brown or flaccid.
Use the prepared zucchini within four days after you store it in the fridge. If you intend to use it without cooking it consider using it even sooner than this.