You should definitely be seeing rise in the sponge by now. If you're not, let it rest another 12 to 24 hours before feeding it again. There should be doubled if not more in size growth. More is better in this case.

Repeat Day Three, that is, discard half, add one cup bread flour and 1/2 cup water. Mix thoroughly, place back in your container and let rise. Check it in the morning, if it's very active you'll be ready to make your barm. It's okay if it triples in size, it will be very soft and spongy, like a poolish. When it falls easily when you tap on the side of the container, your seed culture is done and ready.