Hi Beverly
Incubation does not take place until the last egg is laid. Then, it takes between 30-45 days for hatching. Usually, swans and other birds will not waste precious energy to continue sitting on a nest of non-viable eggs. So, if the swans are still paying attention to the eggs, it usually means that there is still a chance for hatching. Hopefully, you will see cygnets soon. The Regal Swan