I had an egg hatch yesterday that took three broodies to finish the job, because I kept putting eggs in way past the first day. If you have backup broodies, you can try to fool mother nature. If you don't get prepared to see the hen setting on an empty "new" nest she made for herself after she has halfway brooded your eggs and left them setting out in the breeze. Not such a big deal when it is hot weather. I suspect cold weather would kill eggs that sat out for long.