I'm using a cabinet setter incubator with 3 racks, so with chicken eggs that hatch every 21 days I set eggs weekly with 96 eggs per rack. Since I know not all the eggs in the 1st setting will be fertile and I have not one, but three empty racks to start with I decided to fill all three. For this 1st setting of the year I usually collect eggs for two weeks, but collected for three weeks this time to make sure I had enough eggs to fill the incubator. This past Monday I sat 288 eggs. Next Monday when I'm ready to put in my 2nd setting I'll candle the eggs that have been incubating and toss those that haven't started developing. If that doesn't free up the room I need for my 2nd & 3rd settings to go in I'll toss out started eggs with the poorest color, shape, size, etc.