Do you keep a light on over the incubator, someone told me that they will hatch faster if you keep a light on, they think it is time to get up and boogie. It worked good for me! Good luck!
And yes, they do think that, we have a little duckie that decided I am it's mommy, it snuggles up in my neck and goes to sleep chirping and if I chirp back at it, it will start cleaning my hair. It is kind of funny, now when he is 10 lbs it might not be so funny!
I have a stupid question, what sort of egg is it? Some eggs don't hatch in 21 days they hatch in 28 days or more depending on chick or duck or guinea
Is that a homemade bator Cool! you never know but if the temp fluctuates, sometimes it delays the hatch. Be patient and resist the urge to open up the bator and "check" on it! If you have not candled it, you might try that and see if you see a beak in the air pocket in the big end of the egg. If so you are very very close. Just don't mess with it too much. Hold it up to your ear and see if you can hear him pecking at the shell, if so you have about 24 hours max.