Misconception #1: Sundays in Lent are part of the Lenten Season
Misconception #2: Lent is forty days long
Sundays are neither considered part of the Lenten season nor is Lent forty days in length. To explain this requires a little history of Lent.
In the first stage we see that as far back as the year 384 that Lent comprised six weeks and was officially called Quadragesima — literally 40 days. Quadragesima consisted of the forty consecutive days immediately before the start of the Triduum1. This put Lent beginning on the First Sunday of Lent and lasting through Holy Thursday. Holy Thursday was not part of the Triduum and the Triduum was not part of Lent. We know all of this to be true because of the writings of St. Leo2. Even though the preceding forty days were all days of Lent, not all of them were fast days so much as they were days of spiritual combat. Sundays have never been considered days of fast and we can see in the Early Church an Apostolic Constitution3 tell us that a man who fasts on the Sabbath is guilty of sin.
The second stage of Lent happens around the time of the fifth century and lasts until Pope Paul VI’s reform of Holy Week in 1969. In the fifth century we see the development of the Triduum into Holy Thursday - Easter Sunday. In doing this the character of the forty days was changed and, in an effort to maintain the forty fast days, Lent was reformed to begin on Ash Wednesday, which had previously been not part of Lent but rather a day of preparation, and last through Holy Saturday, essentially overlappting with the Triduum. We can look to the Gelasian Sacramentary of this time as it was the first official text to refer to Lent as beginning on Ash Wednesday. It is important to note that at this time in History the forty days of fast overlap with the Lenten season, but this has not always been the case and isn’t the case currently.
The third stage of the reform happened by Pope Paul VI in the year 1969. At this time the season of the Sacred Triddum was restored. Doing this shortended the Lenten season from 40 days to 38 days, if you count all of Holy Thursday. The reform of Paul VI stated that the Triduum would begin with the Mass of the Lord’s Supper on Holy Thursday and Last through Evening Prayer on Easter Sunday. It was also at this time that Paul VI removed the obligation to fast from all days except for Good Friday and Ash Wednesday. Here we have the nature of the fast removed from the Lenten season. This revision returns us back to the original calculation and meaning of the Triduum and Lent. The norms of the Tridduum note that on Good Friday and (if possible) and Holy Saturday the Easter fast is to be observed4. So how to we get 40 possible fast days? You add the 38 days of Lent and Good Friday and Holy Saturday and you end up with 40 possible fast days, though there is no obligation to fast on those days except for Good Friday.
In Concusion, Lent is not forty days long but rather 38. Sundays are not and never have been calcuated as part of Lent. Even the current regulation notes that Lent runs from Ash Wednesday - Holy Thursday, exclusive5 (meaning some days in between are not part of Lent, namely the Sundays.) We also see that from the history that the penitential season of Lent and the 40 days of fast are two separate entities that have not always been one in the same. This is evident from our current practice where the possible 40 days of fast include the 38 days of Lent and two days of the Triduum.
Misconception #3: Beginning at 4pm on Saturdays we being observing the Sabbath and therefore can endulge on what we have given up as a penance.
Not true. There is a great difference between an anticipated Mass and the beginning of the Sabbath observance. An anticipated Mass (which typically begins at 4pm) is a Mass in which the obligation for attendance at Sunday’s Mass is fulfilled. The Code of Canon Law Can. 202 §1, specifically notes that for time calculation purposes begins at midnight. However, the Church has had a long standing custom of observing the Sabbath beginning at evening of the previous day. This is noted in the General Guidelines of the Liturgical Year. Even if we followed this thinking, the Sabbath observance does not begin until true evening, not a set time. This is the same guidelines that are used to calculate when an Easter Vigil mass can be celebrated (which is usually never before 7pm). The point to make is that there is a distinction between the sabbath observance and an anticipated Mass and at the very earliest the sabbath observance cannot begin before evening6. I however, tend to favor the Code of Canon law because it is a newer document and most likely supercedes the 1969 Liturgical Guidelines.
1. It is important to note also that in the General Norms for the Liturgical Year that the Sundays of Lent and Advent are clearly noted as "Sundays of Lent and Avent" respectively whereas Sunday during ordinary time are referred to "Sundays in Ordinary Time." This is even denoted in the Sacramentary which clearly say "Second Sunday of Lent" and "Second Sunday in Ordinary Time" noting that Sundays of Lent are not in Lent.
2. See St. Leo the Great’s Sermon #39
3. 250-300 AD Apostolic Constitutions Do you therefore fast, and ask your petitions of God. We enjoin you to fast every fourth day of the week, and every day of the preparation, and the surplusage of your fast bestow upon the needy; every Sabbath-day excepting one, and every Lord’s day, hold your solemn assemblies, and rejoice: for he will be guilty of sin who fasts on the Lord’s day, being the day of the resurrection, or during the time of Pentecost, or, in general, who is sad on a festival day to the Lord For on them we ought to rejoice, and not to mourn. (Constitutions of the Holy Apostles, book 5)
4,5. General Norms of the Liturgical Year and the Calendar
6. http://www.blessedsacrament.com/theology/emmanuel/huels.html
For More information, see Abbot Patrick Regan, O.S.B’s article "The Three Days and the Forty Days" in Worship #54 (1980). Most of the Information for this article was taken from Abbot Patrick’s article.