Just remember that hatching eggs doesn't have to be exact. If you keep the temps relatively stable, turn the eggs, and add water once in a while, chances are you'll hatch SOMETHING. I have a bad problem with remembering to record when I set eggs, and I also often have eggs set that are from an...
Timing starts the moment you set them in the incubator. If you set them at 8 am on the 1st, they should start hatching at 8 am on the 21st. If you set them at 8 pm on the 1st, they should start hatching at 8 pm on the 21st. Some people count set day as 'day 1' if they were set in the morning and...