The Season of Advent begins four Sundays before Christmas and ends after the mid-afternoon prayer on Christmas Eve.
The Christmas Season begins with Evening Prayer on Christmas Eve and ends with Evening Prayer on the Feast of the Baptism of the Lord.
Ordinary Time begins after Evening Prayer on the Feast of the Baptism of thre Lord until Ash Wednesday.
The Season of Lent begins on Ash Wednesday and ends with the Celebration of the Evening Mass of the Lord’s Supper on Holy Thursday.
The Paschal Triduum begins on Holy Thursday with the Evening Mass of the Lord’s Supper and ends with Evening Prayer on Easter Sunday.
The Easter Season begins on Easter Sunday and ends with Evening Prayer on the Solemnity of Pentecost.
Ordinary Time begins after Evening Prayer on the Solemnity of Pentecost and continues until Evening Prayer of the First Sunday of Advent.
http://stmarymysticalrose.org/liturgical-seasons