I've been waiting until the fourth day before I candle. I can see which ones have babies starting to form. I looked at the first website that someone posted and it's dead on. I definitely wouldn't shake them though! I try to leave them alone as much as possible too. Around day 7-9 I candle again and throw out all the eggs that have no development in them. Once I've done that, I just check every couple of days to make sure there aren't any fresh eggs under them. I've noticed they tend to get a little greedy when they get broody and try to sit on every egg that comes out of every chicken. Good luck, hope this helps!