They can be kept room temp for up to 2 hours but, according to the USDA, they should be refrigerated after that because they contain eggs. I usually let my pecan pie bars cool for an hour or so on the counter and then put them in the refrigerator to completely cool. This makes them much easier to cut into perfect squares and allows the filling to set up completely. I go into more detail about how to freezer them for longer storage later in this article.