How long can potatoes be left out to cool before I make it into a salad?

Karen as long as you just left them out, with nothing on your fine. chill them slice em thin, equal parts mayo sour cream, but not a lot, finely chopped chive or scallion . easy simple , skin on or off your choice. but this refrigerate!

If you did that in a restaurant, it would be a clear health violation. Potato contains everything needed for bacteria to thrive - sugar/starch, moderate pH level, low salinity, and you gave it time and optimal temperature. Any bacterial contamination could have multiplied more than 512 times in 3 hours. It's not safe.

It was completely unnecessary for you to cool them at room temp. It takes less than 10 minutes to completely cool down boiled diced potatoes by running cold tap water over them in a strainer. This is the preferred technique for potato salad so that you can precisely time the cooking of the starch to get the right firmness, then the cold water can arrest the cooking to keep them firm without turning into mush/mashed potato. The potatoes should be parboiled in salted water at a rolling boil, testing for tenderness instead of using a timer/clock, so that you can get the perfect texture and then stop the cooking immediately with the cold water. The potatoes should be evenly diced or sliced before boiling so that they all cook at the same speed. It only takes about 6-8 minutes to cook the diced potatoes to a firm yet tender texture. They will mostly turn to mash if you mix them while they're hot, which is fine if that's what you want, but that's not the result I want. I don't want cold mashed potatoes. I want the flavor and texture of the potato to remain distinct to contrast with the diced celery and onion.

By the way, it's a myth and old wives tale that mayonnaise is more susceptible to food borne illness than other ingredients (like potato). Mayonnaise is actually less likely to be the cause of illness because it has several natural antibiotic ingredients - acidity (vinegar), oil, and salt, and if using mayo from a freshly opened jar, it has been highly pasteurized with a low starting bacterial count. Fresh ingredients are far more likely causes of food borne illness. Using potato salad as an example, of the freshly boiled potatoes, cooled with cold water, then mixed with mayo/salad dressing, mustard, pickle relish, and some fresh veggies like celery and onion - it's the veggies that are the ingredients that are the most likely source of E.coli, salmonella, strep/staph contamination, since they are the only ingredients that aren't cooked.

As long as it was just the potatoes that sat on the counter for three hours (no dressing, mayo, etc) you can use them for your potato salad. There's nothing in cooked potatoes that will go bad if left on the counter for an extended period of time. Once the dressing is on the salad and everything is mixed together you definitely want to keep it in the refrigerator.

If the potatoes were covered, they should be fine.

By the way, one secret to making potato salad is to make it with warm potatroes and then cool it. The dressing soaks into warm potatoes much better than cool potatoes.

It should be safe if it is just potatoes. If you've added other ingredients like eggs and mayo the toss it. But cooling any potatos for 3 hours should not be of worry. The restaurants do it all the time..