On day 22, I pull all the unhatched eggs and break them open and assess the contents.
The only reason not to do this on day 22, but to wait a couple more days, is if you suspect the broody laid a few more eggs after beginning incubation. Then there would be reason to believe there could be a staggered hatch.
I have a broody sitting on eggs right now. I collected the fertilized eggs myself, held them back, then when my broody began sitting the nest in earnest, I then gave her all the eggs. This is how I know all the eggs will hatch on the 21st day. There's no reason to wait any longer for any remaining eggs to hatch.
If there's any doubt in your mind as to the viability of your unhatched eggs, pick each up and listen. There should be audible peeping. You can also candle them to see if there's movement.