The Intercalate, also known as the Division, was an event in which The Sun-in-Splendour was killed by The Forge of Days. This resulted in the ascension of The Madrugad, The Sun-in-Rags, and The Meniscate as Hours (having formerly been Names of the Sun), and also the creation of The Wolf Divided. The Worms bred in the Sun's corpse after the Intercalate. It was foretold in The Book of the Extinguished Heart, as well as in The Time of Division, which said that the Sun would be divided to prevent it from siring children.The Intercalate is commemorated by the Rite Intercalate.
The term "Intercalate" refers to an insertion, especially the insertion of a period of time into a calendar (which would be a particularly appropriate action for a being known as the Forge of Days). The Book of Hours Kickstarter suggests it postdates the War of the Roads, which could imply that it corresponds with the historical Gregorian calendar reform in 1582.