I have something very close to evidence:
Look at this page of the book of Alphonsine Tables: You are not allowed to view links.
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You see the Latin word Radix to indicate the starting point of the computation of each era: the Diluvium era, Alexander era, Cesaris era...
The scribe changes the word Radix. He leaves the letter R but changes the rest of the word and replaces it with a sign that is the same as the right leg of the gallows Eva-t and Eva-k of the VM.
This sign or symbol can only mean noon, since it was the noblest moment of the day and when the computation began. Thus, the Alphonsi era began at noon on the eve of his coronation as king: May 31, 1252.
Therefore, in the VM the Eva-t could mean noon and Eva-k the midnight. Eva-t would be formed with the left leg (Eva-q that goes up the horizon) and the right leg, the meridian.
These gallows and the others would work as starting points. That would explain that they were almost always at the beginning of the paragraphs in the VM.