As long as they are packaged correctly, they should last at least 1-2 months in the freezer. The most important thing to do before freezing is make sure the pizza crust has cooled completely after par baking and you also want your toppings cold or at least not warm. This prevents steam from building inside your container and steam leads to ice crystals. I use regular freezer bags for my pizzas and package 2 to a bag with a piece of parchment in between. You can also simply wrap the pizzas after they are frozen in plastic wrap.