is it normal if some eggs are undeveloped then the other. same incubation day

[IrisJade]

^

 

[littledog]

I'm fairly new to using my new incubator, but out of my two hatches so far, it was about 2-3 days from the first one hatching to the last. The first one was a day early, and went from first pip to out of the egg and walking around in about 20 minutes! The last one started pipping late in the day it was supposed to, but then took like 24 more hours to hatch.
But it's OK to leave the early ones in the incubator while waiting for the others, because their yolk sac provides them enough food for a couple days, before they need food and water.