Refrigerating warm potato salad 13 hours after dinner

Same answer as always: you don't want to eat any perishable food or food for which any part has spent more than about 4 hours cumulative over its lifetime in the danger zone (40 - 140 F, 4 - 60 C).

Do you know how the pizza place treated the calzones before you even received it? It may have been sitting on a shelf at room temperature for an hour or two at the store before you ordered it, in addition to the transport time when you took it home, and all the times as you heated and cooled it when it was in the zone.

In general to reduce the quality degradation, and the amount of time food ends up moving through the danger zone, you normally only want to heat up the portion of food you intend to eat, and leave the rest refrigerated.

See also: https://cooking.stackexchange.com/tags/food-safety/info

In an ideal world, you would chill any hot food product rapidly before putting it in the refrigerator. However, modern refrigerators can handle the load from a mass of hot food, so it is better to put the food in the refrigerator than to hold it at room temperature to cool.

The goal is to minimize the amount of time in the danger zone (40-140 F, 4-60 C) during which pathogens can grow.

See also:

• What are some techniques to cool down a dish so that we can store it in the refrigerator safely?

• How effective are modern home refrigerators at keeping other foods cool when hot food is introduced to the space?

• How do I know if food left at room temperature is still safe to eat?