Glad you could join us here! The embryos will not start developing until they have been set in the incubator. Day 1 is counted after a full 24 hours of incubation so say you set on a Monday at 9am day 1 would be Tuesday at 9am day 2 would be Wednesday at 9am and so forth.
Here is a fab article on incubating that I'm sure you will find most helpful ~ https://www.backyardchickens.com/a/hatching-eggs-101
Wishing you the very best of luck with your eggs and enjoy your time here on BYC