Congratulations. Sounds like you are doing great.
There were two possible things off in your incubation. Both have been mentioned but I don't think one was explained fully. If your incubator is running a bit cool, they will be a bit late. I think that was covered well. But before you start adjusting the temperature, you need to make sure the day count is correct. Kedreeva is correct.
I don't like using day 1, day 2, etc. That messes up a lot of people. An egg takes 21 full days of development to develop 21 days worth. An egg does not have 24 hours worth of development the instant you put it in the incubator. It has to be in there a full day before it has a full days worth of development. If you are going to candle an egg at day 8, for example, you need to wait until 8 complete 24 hour time periods have passed. If you candle the egg 7 complete days and 1 second after you start incubation, you need to look at the 7 day picture, not the 8 day picture.
Let's assume you set the eggs at 8:00 a.m. on Thursday, July 1st. Lockdown should be 18 full 24 hour periods later, which would be 8:00 a.m. Monday July 19. Hatch should be at 8:00 a.m. Thursday July 22. With chicken eggs, the day of the week that you start them is the day of the week they should hatch. If you start them on a Thursday they should hatch on a Thursday.
They are tough little things. I had my incubator running a little hot and locked down after 18 full days. I had my first chick hatch a day and a half later, a full day and a half early. Although my lockdown was late based on incubation temperature, I still had a good hatch. Here's hoping yours is also a very good hatch.
