A Bit of a Silly Question

[bangarain]

Hello! This is my first time incubating eggs, and they're all in!

My incubator has a day countdown built in, which is great, but I'm uncertain as to whether I should set the 21 days from today, when I set the eggs, or tomorrow, when they have had an entire day to incubate. Which is correct?

 

[Chickens are awsome]

If you set it at 21 days your incubator should(haven't used that brand) go 24 hours before changing to 20 days.