it is illegal in NZ to sell fertilized eggs for human consumption. Any eggs from the supermarket will be infertile.
If you want to hatch some chicks, buy fertile eggs from trademe.
On another note, a fertilized egg will survive a couple of weeks in the fridge before beginning incubation. This is because when a hen builds a nest, she will lay one egg per day, and only start to sit on the eggs once she has a full nest of eggs. this means that even though the eggs are laid over a couple of weeks, they all start developing at the same time, and as a result they hatch at the same time.