Have you been candling along the way? These are Coturnix quail? You should be in the lock down stage, not turning the eggs, and have your humidity up to around 65% or 70%. If your temp was a hair lower than it should have been during the entire cycle, the chicks develop a bit slower and can hatch late. Sometimes 3 or 4 days later than the expected date.
They are coturnix. I haven't been candling but did stop turning on day 14 and haven't opened the lid since then. Added some water on day 14 to try to keep humidity up. I've seen the heat up a little but not down. I am just a little anxious hoping I did everything right. I down have anything to tell me what the humidity is though.