Seen one jump today
Hold it up to your ear and talk to it, mine will usually answer me around day 25 -27. If they do, it means they have made the internal pip into the air cell and they should make the first pip of the shell soon. At this time it is important to raise the humidity as high as possible, I like mine around 90% for the last 3 days only. This will keep membranes from drying out and sticking to the chicks, sticky membranes can prevent them from hatching.