I went to pull some queen cells out of a hive I knew had not started them, but I didn't have time to pull them out and find a frame to replace them so I left it. Two weeks later I pulled them out to use them and the queen had layed in them and they bees had started about four of those and they looked like about one day old larvae. I was grafting larvae the same size. Being transparent plastic, I could see the level of royal jelly in the cups and the larvae the same age as I was grafting had 1/8" of royal jelly filling the bottom of the cells. The contrast was amazing.