In continuous warm conditions (22 – 26°C) the eggs of most Australian phasmids will begin hatching around three months after being laid.  If you do not have the eggs in an incubator and they experience some cooling, then the incubation period will often be extended. Some eggs will enter a state called diapause where they do not continue to develop until they are stimulated by other factors. Favourable seasonal conditions such as warming and increased humidity are often the stimuli they require. Minibeast Wildlife has recorded Extatosoma tiaratum eggs hatching three years after being laid, when they experience seasonal cooling.   Soaking the eggs briefly, then warming them with increased humidity is a good way to stimulate hatching for eggs over three months old.