Salad can last up to 2 hours at room temperature before it starts to go bad.
If the salad has any meats in it you should keep it refrigerated until ready to eat because the meat after 30 minutes or so of sitting out could start to grow bacteria and go bad.
But if the salad has no meats it can safely last up to 2 hours at room temperature but keep the salad refrigerated keeps it fresher and makes for a better salad.
However if the temperature in the room is hotter than 90 F then the salad may start going bad after 1 hour.