No more than 2 hours to be safe!!
This is absurd. Who is answering these questions, a child???
According to the usda's website....If ground beef is refrigerated promptly after cooking (within 2 hours; 1 hour if the temperature is above 90 °F), it can be safely refrigerated for about 3 or 4 days. If frozen, it should keep its quality for about 4 months.