The worlds in the novel have very long days, much like our Moon does, about two weeks daylight, two weeks nighttime. Their inhabitants, both man and beast, have adapted to that cycle by hibernating during the night. However, would this be really possible for humans or, in general, for viviparous mammals? It should be Ok for adults but what about babies?

Babies would have to be born early in the day, which should not be much of an issue. When the baby is ready, actual delivery is triggered by hormones and part of the adjustment to the day/night cycle would be to generate those hormones. During their first day babies would need to grow and gain enough weight during that first daylight period to survive their first hibernation. Maternities would have a really hard job early every morning, with all expecting mothers due on that day giving birth to their child almost all at once. The later in the day a baby was born, the less likely he would survive.

Unless, of course, they are neither viviparous nor mammals.

I didn´t think making our characters too alien would add much to the story, thus I made them very, very human. However, I never said they weren´t born from eggs.