It is not recommended to keep a tampon in for more than 8 hours, as this can increase the risk of toxic shock syndrome. Symptoms of this syndrome can appear after 3 to 5 days of tampon use. It is important to change tampons every 4 to 8 hours to reduce the risk. If you experience symptoms such as fever, nausea, vomiting, diarrhea, or confusion, it is essential to seek medical help immediately. You can find more information on this topic from the Government of Canada's website.