The progression of seasons.
The phases of the moon
The length of pregnancy.
All of these can force certain events in a story to be thus far apart, and all the other events have to take that into account.
Am currently wrestling with a journey, and whether the returning travelers can learn that a woman became pregnant shortly before they set out.
It makes me very glad that I didn't include one of the fairy tales where a woman has three children in successive pregnancies. Now that would lock the story onto a rack.