No need for the crabby remark, nuthatches. I think the OP has some confusion how this works.
Once in a great while you will have a hen slip off to a hidden nest, lay an egg, and go back day after day, until she likes the nest, and then she settles in and is 'broody'.
At THAT time, once the eggs have been heated to about 100 degrees, for 24 hours, THEN they begin to develop into chicks. That way all the eggs hatch together.
Domesticated birds, often times just get the urge, and become broody. We notice them, when they pancake out, growl at us and do not leave the nest.
After the hen has settled for a day or two, I mark my eggs with a sharpie, and give her a clutch, all at one time. These eggs will hatch within hours of each other. The problem with a staggered hatch is that once she has live ones, she will leave the nest with the live chicks and move back into the flock. The late eggs, still not ready to hatch will die.
So adding eggs later is not a good idea. Also you need to limit the number of eggs you add. A hen stirs them up, moving them around. If there is too many eggs, the ones on the outer edge are not warm enough, and die in the shell, then she stirs them up and new ones are moved out to the edge, and you wind up with very poor hatches.
Personally, I don't lock mine in. Mostly I leave mine completely alone. Generally, I check every 2-3 days, to make sure stray eggs have not gotten in there. People worry about water and feed, but the life force is enough to get them out for food and water.
Mrs K