The Minor Litanies—Rogations—are today. If the Rogation Mass is not celebrated, it is not commemorated in the Mass of the day (except on April 25, which regards the Greater Litanies), and the Rogations are not included anywhere in the Office.
The Minor Litanies (excerpted from Rubricae generales):
82. According to conditions and customs varying from one church to another and from one place to another … a procession is held on this day, in which the Litany of the Saints is said with its accompanying prayers. The petitions of the litany are not doubled.
83. If a procession cannot be held, … special supplications [may be said], which shall include the Litany of the Saints and the other prayers customarily said in procession.
86. The Rogation Mass is regularly to be said after the procession…. It is fitting, however, that the Rogation Mass be said even after the special supplications which take the place of the procession, even if these services are held in the evening. [It is a II class votive Mass, per RG 346.]
87. The minor litanies or Rogation days, of themselves, are assigned to the Monday, Tuesday and Wednesday before the feast of the Ascension of our Lord.
88. Of the minor litanies there is nothing in the office, but only in the Mass which is connected with the procession or with the other special supplications.
90. On these days the Litany of the Saints with its prayers is said only in procession or as part of the other supplication…. Hence, those who are bound to the recitation of the divine office but do not take part in the procession or in the other special supplications do not have to say the Litany of the Saints with its prayers on these days.
Apart from procession/supplications: Mass of the preceding Sunday, Gloria, no Credo, preface of Easter
Following procession/supplications: Mass of the Rogations Exaudivit de templo, listed in the Missal before the Vigil of the Ascension (Violet), prayers at the foot of the altar omitted, no Gloria*, no Credo*, preface of Easter
*The Gloria and Credo are not said in the Rogations Mass because it is a II class votive (no Credo) with violet vestments (no Gloria)
The Minor Litanies are not commemorated in the Divine Office.
Matins: Invitatorium and Hymn in Tempore Paschatis, antiphon Alleluia and psalms of the feria, three lessons from occurring Scripture, Te Deum
Lauds: Antiphon Alleluia and psalms of the feria (first schema); remainder in Tempore Paschatis; Benedictus antiphon and oration proper
Hours: Antiphon Alleluia and psalms of the feria; remainder in Tempore Paschatis; oration proper
Vespers: Antiphon Alleluia and psalms of the feria; remainder in Tempore Paschatis, Magnificat antiphon and oration proper
Compline: Of the feria