The world on which Ophelia and Lyan live, called Honua, isn't earth in the ancient past or extreme future. It is an entirely separate world.
Case in point, Honua doesn't have a "leap year". The closest equivalent that they do have is called the "Longest Day". Every four or five years, there is one day where, just as the sun starts to set, another starts to rise. So the entire world has a full day and a half of sun before darkness actually falls again.
It's difficult to predict just when it will happen precisely, but it does consistently occur in that four to five year window. Both those factors make it a popular but elusive astrological phenomena to try and tie to rituals or energy manipulation required for the most powerful spells.
This is, of course, only one of many of the differences of Honua and this world. While it does have a lot of elements that fans of fantasy will recognize but there are so many more that are completely new. I'll be mentioning or showcasing various elements here and, of course, in my novels and other works. Please keep an eye out!