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.
Listen carefully and you'll be able to hear faint peeping coming from the eggs in the incubator about 24 hours before the hatch. It takes about 24 to 48 hours for duckling to emerge, wet and exhausted from the shell. The newly hatched babies should remain in the incubator four to 12 hours longer to dry off.