Are the eggs in an incubator or under a hen? If you know what day incubation started (not the day the eggs were laid) chicken eggs should hatch approximately 21 days later. You can candle them with a strong flashlight and compare to a egg candling chart online to see if they appear to be developing as they should.
Don't bug her and let her do her thing, they know what they are doing. count from day aft4eer she starts counting and just watch and make sure she's getting enough food,water,stretching and pooping outside of the nest area, it is normal for a hen to get off nest 1-2 times a day up until about day 18.
Note if it is warm where you are she may be off for more time without any problems,mine are usually off anywhere from 5-30 minutes depending on outside temps
if she doesn't get off she doesn't feel safe enough to do so, is there anyway to block access to her nest? I would say then you would have to take her off at least once a day or partition of an area where she can get off the nest and feel safe doing so and add some food and water outside in the partitioned off area. this is so she doesn't get nest dirty and she can eat and drink with less stress and see if that will encourage her to get off on her own.
there was an egg this morning on the other side of her nest and it was freezing cold to the touch and obviously dead and I took a look in it and the chick was all the way developed except the yolk was not absorbed into it. how old does that make it?