I'm cooking 3 frozen pot pies do I need to adjust my temp so that they will cook in the hour it takes to do just one
In general ovens are not adjusted for the amount of food being cooked. It really only matters if you oven is not good at holding temperature, if a very large mass of cold is being heated or if there is enough in the oven to block air movement. An oven tends to act as a large heat reservoir with a relatively small food item being cooked. Three small food items will tend to cook in about the same amount of time as one. You might see a little difference, but it is unlikely to be a huge jump in time needed. It is different when applied to something like a roast or turkey where a 20 pound item will take much longer than a 10 pound item.
When heating something in a microwave though, this is not true. A microwave oven focuses the energy and the items in it take that energy without there being a heat reservoir. So, if you attempt to cook 3 items at once rather than 1 you need to provide much more energy, which is done by greatly increasing the time, or simply reverting to doing one at a time.
In the case of conventional oven, I would not really expect a need to increase time by more that a few minutes, if at all, but there cooking times are always approximate in any case. The true answer to if the item is heated enough is always temperature, not time.