No matter how delicious it was yesterday. If it was out in the sun all day. Toss it.
The food danger zone for perishable food is between 40˚-140˚f. Do not take a chance with that Fantastic Potato Salad, Baked Mac-n-Cheese, Chicken Wings, etc unless they were stored back into refrigeration within 90 minutes after being prepared. Depending on the temperature during the day in your area, that 90 minute mark maybe pushing it. Food can spoil right after it has been prepared. Bacteria growth can get rise while that food sits in that danger zone.
Potato, Egg, Chicken, Tuna or any Salad with mayonnaise can hold in bacteria if it was sitting in the hot sun all for an hour+. So if you are not certain if something went bad or not, throw it out.
That is why the saying is ‘Serve hot food hot & cold food cold’.
Keep this in mind for your next summer buffet and try to serve the salads over an iced container or use chaffing dishes for that hot food. Try to remove them after everyone has had a plate or two. If they get hungry later, they know where the refrigerator is. They can help themselves.