Slow to hatch?

I have a GQF incubator and brooder. Basically the brooder is a incubator without the turner in it. I have eggs in the brooder ready to hatch. They were to start Weds, and had one start last night, but it was breach and also under developed. But I do have one little black one this morning that is healthy. I candled all eggs before I put them in the brooder. Could I just be a little off on timing? Or could they just be slow to start hatching. I did not move them from the incubator until 3 days before they were due to hatch. Guess I just expected to see more little ones by now. I have never had one of these big incubators or brooders. Guess I am just paranoid that I screwed up the hatch.

 

Thanks for the info. I have only been opening when I need to add water. I check the temps, and both have stayed steady at 100. I have one baby hatched, and hear others beginning to peep. I had always had the small still air incubators. So, just worried about having everything right with this automated stuff.

Thanks Again!