It is best to give them 3 days past the usual hatch day. The usual hatch day is 21 days after she FIRST started setting on the eggs.
If eggs were added by another hen or you AFTER she started setting, you could have a staggered hatch. That would be where chicks are still hatching days and days later while she is caring for the chicks.
It is vital to put food and water RIGHT next to her so she doesn't have to get up from the nest to eat and drink if you want her to set further.
She has to teach the babies to eat and drink.
Also- if you have a very strong flashlight you can look inside the eggs to see if they are clear (no baby) or dark (baby alive or dead).
She started sitting April 30. Believe it or not, my daughter won these eggs in a raffle at a poultry show. We had a salmon favorolle hen that kept going broody so we let her sit on them, so we know they all started at the same time. Thanks for your help! Sounds like Monday evening is the stop date. Besides, no more are pipped.