Here's a little more info about the Little Office of Our Lady. Hope it helps fill out the Wikipedia article. It's a truncated form of the Divine Office which, in its traditional form, consists of the eight traditional canonical Hours (Matins, Lauds, Prime, Terce, Sext, None, Vespers, and Compline). Each hour is much like the Roman Office in its structure -- psalms with antiphons, a hymn, a Scripture reading (three at Matins), a versicle and response, a Gospel canticle at some hours, and a closing prayer.
Overall, though, the Little Office of Our Lady differs markedly from the Roman office in that it is basically the same every day. Here are the variations (I'm working from memory here so this might not be completely accurate):
- There are three nocturns (i.e., sets of three readings or "lessons") given at Matins, but only one nocturn is used each day, and the choice of nocturn is determined by the day of the week.
- The psalm antiphons and the readings and versicles/responses vary during Advent and again during Christmas
- There are minor variations throughout during the Easter season
Perhaps needless to say, the psalm antiphons, lessons, versicles, and orations are very pointedly Marian -- and sometimes very intriguingly so, since they're frequently direct quotations from Scripture, but not necessarily from a part of Scripture one would immediately associate with Mary.
The psalms themselves don't change from day to day, or seasonally as far as I'm aware, so the entire Little Office of Our Lady includes only 20-30 psalms.
If you happen to be interested in older forms of the Western Liturgy of the Hours, this little office is an excellent introduction because it's so simple.
It seems to have been hugely popular among the literate laity in medieval England (pre-Reformation), and AFAIK it's still prayed daily by Carthusians "in cell" as an adjunct to the great Office. E.g., before singing "great" Vespers in choir, a Carthusian will pray the Vespers of Our Lady alone in cell.