In this world there is no moon, so there are no months.

Instead, the four seasons are divided into ‘thirds’, each lasting thirty days. To make the year up to 365 days, five extra days are added, two between winter and spring, and one between the other seasons, roughly corresponding to each solstice and equinox.

New Year starts on the vernal equinox (our 21st March).

— New Year’s Day – 21st March
– First Third
– Second Third
– Last Third
— Summer’s Day – 20th June
– First Third
– Second Third
– Last Third
— Autumn’s Day – 19th September
– First Third
– Second Third
– Last Third
— Winter’s Day – 19th December
– First Third
– Second Third
– Last Third
— Year’s End – 20th March

Examples:
Daphne’s fort was built in the last third of spring (i.e. our 21st May to 19th June)
The goat gave birth on the fourth day of the second third of autumn (i.e. our 23rd October)