I bought a 100 gallon stock tank on Friday and filled it with water and will be using it as a pond in my backyard. I've added some plants and a couple of trapdoor snails. I made a homemade sponge filter using sponges from my tropical aquariums indoors. Hopefully that won't kill the bacteria going from a high temperature to a much lower temp.... 78 down to about 60 I would think. Anyway, I would love to be able to add two Sarassa as soon as I can. Can I add them tomorrow or do I have to wait longer?

Is this a rubbermaid stock tank or metal? I assume the first. The metal ones can be dangerous for fish. Does your sponge filter create aeration as well? If the new water is fully aerated, then it should be safe to add a few fish to see how they do. The longer that you wait up to a certain point, the more microorganisms, insect larvae, algae, etc. will be in the pond making it more hospitable for new fish. Other than that, you want to be sure the water is aerated, safe, and stable and all your electrical things are working right before adding the fish.