An internal-combustion engine needs four things to run. They need fuel, mixed with air, in a ratio of 14.7 to one. An ignition-spark lights the fuel and air mixture, creating combustion. Compression of the fuel and air mixture makes it explosive. The final necessity is proper timing, of the components.
1 The length of time it takes for eggs to hatch after incubation begins depends on the species and temperatures. 2  For bluebirds, it USUALLY takes about 12-14 days from the date the last egg was laid.3  Different species have different incubation periods, which can vary within a species due to temperature inside the nestbox. Depending on when incubation begins (on the last, or next to last egg), eggs in the same nest can hatch a day or several days apart. 2  It also takes a while for the bird to break through the shell. 3  It could be a new egg from a subsequent nesting if you didn't clean the box out immediately after the last fledging.
A mother duck sits on her eggs for 20 to 23 hours a day, taking an average of three breaks, each lasting around an hour at a time. When she does leave her nest, the duck hen covers her eggs with additional down and nesting material to help keep the eggs warm in her absence. The incubation period lasts an average of 28 days, about a month. With the mother duck spending so little time away from the nest, she relies on stored fat to survive. A couple of days before the eggs are ready to hatch, small cracks begin to appear, and the ducklings will begin peeping from inside their eggs. Then, in a span of 24 hours, all the ducklings will hatch from their eggs, using a small sharp bump on their bills called an egg tooth..