Cooked hamburger should be refrigerated within two hours of cooking. Any cooked hamburger or other perishable food that has been left at room temperature for more than two hours should be discarded.
Following food safety recommendations is important in preventing foodborne illness. All forms of ground meat, including hamburger and ground beef, lamb or veal, should be cooked to an internal temperature of 160 F. Once food is cooked, it should be kept at a temperature of 140 F or higher. This prevents the food from entering what is considered the "danger zone," a temperature range between 40 and 140 F. Bacteria grow quickly in food in this temperature range, and therefore it should be avoided.