The health code takes effect immediately, which means that the green health code is effective. Of course, as long as you have never been to a high-risk area, your health code will always be green, so don't worry about discoloration. The health code is valid for 15 days. If it takes four or five days, your health code will be invalid, and then scanning the code will become 15 days. Therefore, the health code expires within one month and after 15 days.