Matins, the night hours of the Liturgy of the Hours, is properly done as the first hour of prayer for every day of the liturgy of the hours, in conjunction with the first vespers on Feasts that have first vespers (e.g. Sundays, etc.).
In light of that, if you want to be true to the respective hours of prayer in the Liturgy of the Hours and you do not plan on breaking up your nightly sleeping hours you should anticipate Matins the previous evening and not leave it as part of the prayer of the next day. That would defeat the entire sense of a Vigil prayer. You would not be being vigilant if you wait to the day to say it!
What is more, in the Bible the night hours of prayer are called the "watches of the night" which have exactly that sense I have indicated above: vigilant prayer of the night.
The 1962 breviary therefore allows that Matins be done anytime after 2 PM of the Vigil (same with Vespers).
So, the proper time for Matins would be to anticipate it! Sunrise it too late, for it is time for Lauds and Prime. You are allowed to do Matins the day of (until midnight), but it is not the proper time according to tradition and the logic of the liturgy of the hours.
To habitually leave Matins (The Office of Readings) for the day of and not anticipate would be just as out of place as doing the whole office including Vespers and Compline in the morning (which is allowed but not optimal because out of it's normal hourly place).
N.B. This principle of anticipating Matins is especially important with the traditional 1962 breviary because of the increased length of Matins (especially on Feasts which includes three nocturns instead of the normal one) and of the entire daily breviary in general. On Feasts as a parish priest it is sometimes a struggle to get Matins in and it is very helpful to have 34 hours in which to accomplish it.
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