They will lay eggs in the same box throughout the day. Sometimes our girls line up and start squawking if someone is taking too long, or they will try to sit on top of the girl that is still on the nest. I have morning layers, afternoon layers and one who waits until I have gone inside to lay in...
I have had up to 20 laying hens at one time, and even though we have 10 boxes, they only use 2, sometimes 3 boxes. Ever. They like to lay their eggs in one box. If you are providing the boxes for brooders, you might want 4 boxes, but 2 is more than enough. Enjoy! :)