All of the traditional ceremonies are set up around a yearly cycle of cosmic events and are designed to help the different planets, the sun, the moon, etc. to stay true to their paths and fulfill their destinies. Without the cycle of ceremonies and the participation of the people, things start to get confusing and things don't evolve into their natural patterns. The world may just end. Every detail is done according to a plan concieved long ago by the ancients who, in their wisdom, set up this pattern as a way for everyone to live. The following list is taken mostly from Religion and the World View in Santiago Atitlan by E.M. Mendelson in 1956, and a lot of the cofradias aren't working anymore (their part of the ceremonies has been absorbed by the remaining cofradias) so the information is probably out of date
Ritual Cycle of the Atitecan Year
Date
Occasion
Cofradias
Other Implications
January 1
Año Nuevo
Santiago, San Martin
Election and confirmation of political officials
January 6
San Gaspar or Los Reyes
Concepcion, Santa Cruz, Santiago
Election Santiago. Municipality entertains the procession
January 15
Esquipulas
Concepcion, Esquipulas Particular
First sowing of corn
January 20
San Sebastian
Second sowing of corn
February 5
Fiesta San Felipe
San Felipe, Concepcion, Santiago, San Juan, San Antonio
Third sowing. Misa de Pricipales and rain costumbre. Corn blessing
Feb 20- April 5
7 fridays of Cuaresma
Santa Cruz, San Nicolas
First Friday: 2nd Mexicano practice
March 19
San Jose
San Jose Particular
Semana Santa
Mainly Santa Cruz, but all of the cofradias are active
Sabado de Gloria: 3rd Mexicanos. Participation by the municipality
May 3
Fiesta Santa Cruz
Santa Cruz
Fourth sowing, decoration of crosses
May 14
Acension
Santa Cruz
May 20
San Bernadino
Fifth sowing
June 4
Corpus Cristi
Santiago (Sacramento),San Juan, San Antonio
fourth Mexicanos.Negrito dance from Cerro de Oro, Padre Eterno procession
June 13
Fiesta San Antonio
San Antonio, Santiago
First visit by Santiago to his new cofradia
June 24
Fiesta San Juan
San Juan, San Martin
July 25
Fiesta Santiago
Santiago, San Juan, San Antonio
Ladino festivities
Sept 8
Maria Entividad
San Antonio
Sept 10
Fiesta San Nicolas
San Nicolas
Sept 29
San Miguel
Santa Cruz (Maximon)
Oct 7
Magdalena Castellana
Santa Cruz
November 2
Todos Santos, Fiesta Animas
Animas, San Martin
November 11
San Martin
San Juan, San Martin Particular, San Nicolas, San Antonio
designed to help the different planets, the sun, the moon, etc. to stay true to their paths and fulfill their destinies. Without the cycle of ceremonies and the participation of the people, things start to get confusing and things don't evolve into their natural patterns. The world may just end. 
Every detail is done according to a plan concieved long ago by the ancients who, in their wisdom, set up this pattern as a way for everyone to live. The following list is taken mostly from Religion and the World View in Santiago Atitlan by E.M. Mendelson in 1956, and a lot of the cofradias aren't working anymore (their part of the ceremonies has been absorbed by the remaining cofradias) so the information is probably out of date