Actually, a fishless cycle can be done in 2 weeks. If the ammonia is still reading 0, you need to add more. Since you're doing a fishless cycle, you can bring the ammonia way way up. Since I guess you're using food, don't put a little in there, dump it in there! This is going to cause you to have to clean up a lot of gunk from the substrate, but that's how the ammonia is going to build up. I've always just used pure ammonia, you can get it in cleaning isles at grocery stores.