How long can cooked food straight out of the oven be left sitting out safely before refrigerating it?

It has nothing to do with the amount of time it is left out.  Bacteria grows quickest in food at 40-140 degrees Fahrenheit, basically the entire time it is not cooking or in the refrigerator.  The sooner you refrigerate it the better off it will be.  You did cook it fully, so you do have some leeway since that should have killed any chance for bacteria growth but that depends on how clean your kitchen is.  

Here's another cheery thought for you - how many  of your favorite food place do you think keep their hot foods above 150 degrees and their cold foods like lettuce and tomatoes below 40 degrees?  Now you know why home cooking doesn't just seem better than fast food or restaurant food, it usually is since you have everything at more of an immediate use and less chance for bacterial growth to set in.

Just put it in a turned off microwave to keep it warm. 

In my house, I wouldn't let it go unrefrigerated for more than 2-3 hours.

I worked at a supermarket and we were told things that were refrigerated could no longer be sold after 30 minutes in normal air temperature. Obviously something from the oven will need to cool down first. So I'd say no longer than 1 or 2 hours

Until you want to eat it - surely you intend eating it the same day?

It could be left for several days without being refrigerated. That always happened before folks had refrigerators.

Cover it with some foil, and it will be fine to leave it for a couple of hours or so.

In my home, 8 hours is no problem.

It will be fine. It's fully cooked. Your only problem is going to be that if you tent it with foil, it will continue to cook. If you don't, it will be cold. 

It will be fine until you are ready to eat it, just tent with foil - 2 hrs is BS way too conservative. 

Two hours maximum at room temperature.