Those that hatched 48 hours ago will certainly need swift access to crumbs and water. Are the eggs a mix of breeds? This can certainly lead to a variation in length of incubation time. If your hatching period is, say, four days, it would be worth considering adding more water to prevent the egg membranes drying out. I was advised not to add water at all by Shaun Hammon of the Wernlas Collection, as it tended to make the chicks too big to pip the eggs, but I know a lot of folks do so.