The time it takes for baking really varies based on the actual temperature calibration of each individual oven (sometimes if you call the power company they will come out to measure and adjust to get accurate temperature versus what the dial says, often doing this for free) and the size of the potatoes, but usually 1 hour at 400 degrees F. Larger potatoes take longer.

Do you know what carton count size you are ordering or how many fifty pound cartons for the 250 servings? 

Cost and Size Guide  

I would recommend the 400 degrees F rather than 500, especially if baked in foil. The higher the temperature, the faster the outer bottom of the potato cooks and turns brown by the time the inside middle is done. A lower temperature allows for more even cooking.

One really good method is to bake the potatoes without foil, remove each with an oven mitt and then wrap in foil to retain the heat. The potato is about 80% water so not baking in foil allows the steam to escape.