Fr. Petras' Typicon contains the following note:
During the Great Fast, the daily cycle runs from Matins to Vespers. The commemoration of the saint of the day, however, follows the system of the rest of the year, from Vespers to the Ninth Hour.

This comment has always baffled me, since the texts in the Triodion contain the theme of the "following" day. For example, the stichera at the Lamplighting Psalms on Wednesday evening refer to the Apostles, those on Thursday evening have the cross as a theme, etc. This seems to contradict his first statement, and I can think of no way to reconcile the two.

Wednesday of last week (2/24) the Presanctified Liturgy also contained readings for the Finding of the Head of the Forerunner, which was the saint of the day that was ending, not of the next day, which seems to contradict the second sentence quoted above. I assume this selection of the text for the saint of the day just ending was because of the poleleos ranking of the feast.

But in such a case which saint should have been commemorated at the Lamplighting Psalms? John (2/24) or Tarasius (2/25)? Based upon the commentary in the Typicon for March 9, I'm assuming the stichera for John. Does that mean that those stichera would have been used on both 2/23 and 2/24?

I am so confused.......

But

The new day "begins" at vespers; but more specifically, at sunset. Represented by the ligting of the lamps. So one could say it changes during vespers. Vespers both starts and ends the day.

Yes, I know. That is the point of Fr. Petras' second statement: The commemoration of the saint of the day, however, follows the system of the rest of the year, from Vespers to the Ninth Hour.

But this does not explain the first sentence: During the Great Fast, the daily cycle runs from Matins to Vespers. If, during the Great Fast, the saint commemorated at Vespers is the saint of the upcoming day, and the theme celebrated is the theme of the upcoming day, then how is this different from the system of the rest of the year? The assumption is that these sentences are actually trying to communicate a point and are not merely a nullity, but I am unable to see the point.

By way of specific example, this year February 16 fell within the Great Fast. With a little digging, I'm sure I could find a year where February 16 also fell on a Tuesday but was not wihtin the Great Fast. How would the celebration of Vespers differed from the celebration in that other year?

Ed, the difference is that in Lent you have the intersection of the Triodion, the Menaion, ascetic and Communion fasts that occurs at no other time of the year in this way. The Presanctified occupies a unique transitional place that includes a commemoration of the coming day but does not forget the day coming to a close with the breaking of the fast in receiving the Holy Mysteries.

So taking an example from the New Calendar this week, for example, at Tuesday evening's Presanctified we sang four stikhera of the 40 Holy Martys of Sebaste, while the previous (Monday) evening (here using Dolnytsky's usage) there would have been only three stikhera for the Holy Martyrs with three from the Triodion (assuming Vespers only on Monday evening as we celebrated).

The Old Testament readings were done Monday night both from the Triodion (Genesis and Proverbs) and following these, in addition one from Isaiah and two from Wisdom from the Menaion were taken. The Epistle and Gospel, however, were read at Tuesday night's Presanctified, when in reality at other times of the year that day would have ended liturgically speaking with the Prokimenon of Vespers already having been chanted.

So my guess was right that it is really only an issue when a feast (I'm assuming polyeleos or vigil rank) is involved? The "liturgy" aspects are for the day just ending and the "vespers" aspects are for the day upcoming?

In my experience, the best way to avoid confusion in this area -- especially during Great Lent and Great Week -- is to embrace the Mystery. When we enter the church, we leave chronos behind. Our watches and calendars become meaningless devices. We enter kairos, the Eternal Now, and exult in the Presence of God.

Try it. You'll like it.

Precisely - at last night's Presanctified we took the Menaion stikhera texts for today (St. Sophronius) instead of those for St. Codratus and Companions; neither are doxology or polyeleos rank.

The 40 Holy Martyrs is a polyeleos-rank feast, and as such the vigil Old Testament readings and festal stikhera were taken in their normal place the evening before the feast (Monday, the evening of March 8th) celebrated as Vespers alone without Presanctified. On the evening of the feast itself, since the appointed Eucharistic liturgy is that of the Presanctified, the proper Epistle and Gospel are added to the Old Testament readings normally taken from the Triodion. The same is true for the 1st and 2nd Findings of the Head of St. John the Baptist, and in most usages when the parish patronal feast falls during a weekday of the Great Fast.

The exception, of course, is the Annunciation being one of the 12 Great Feasts and being of Vigil rank. That's yet another different dynamic of intercalation.

That's not a bad theory, unless you are going to be standing alone at the kliros and don't want to constantly have one eye on the liturgical texts and one on a Typicon. And let's not discuss the potential for trainwreck if one's Typicon is ambiguous or inartistically worded.