How long does it take to cool 5 lb of deep fried chicken from 350 degree to 75 degree
What size pieces of chicken? How are they arranged? 

In order to cool quickly, you need to spread the food out in as thin a layer as possible, preferable with space between pieces. You may also require a more active cooler for the chilling process with a larger cooling unit and a more powerful fan - chilling hot food is a far more difficult task than holding cold food.

But the most fundamental step is spreading the food out on trays so it is only one piece deep - that will cool much faster than a basket or tub of the same meat at the same starting temperature. If the tray is metal and is stored in the freezer before use, it would add just a bit more cooling.

Another approach would be to place the meat in a sealed bag (still in one layer), and plunge it into ice-water for rapid cooling.