A: Chopped or sliced onions can be stored in a sealed container in your refrigerator at the proper temperature of 40°F or below for 7 to 10 days (Source: USDA). For pre-cut fresh or frozen products, always use and follow manufactures use by dates.: Chopped or sliced onions can be stored in a sealed container in your refrigerator at the proper temperature of 40°F or below for 7 to 10 days (Source: USDA). For pre-cut fresh or frozen products, always use and follow manufactures use by dates.