Most insect have a particular time of day at which they emerge, but often in response to a specific stimulus. Certain dragonfly larvae hatch in response to water of a certain temperature wetting them. Grasshoppers in response to mechanical disturbance, so if one egg hatches, all the rest laid with it will also hatch at same time. Sometimes an egg instead of producing only one larva, can produce two or more. This is common in endoparasitic insects , where one egg can result in 1000 offspring.
Many species retain the egg in the genital tract until it is ready to hatch, and lay it then.
This is true of many cockroach species. Developing embryos obtain some energy from parent in addition to or instead of from yolk. These are termed viviparous. The young are produced at various stages, the ultimate being tsetse flies which are retained in female until ready to pupate. Aphids and some earwigs are also viviparous.