The Monday Office hymns, "from the Оctave of the Epiphany until the 1st Sunday in Lent"

From Hymn melodies for the whole year from the Sarum Service books, for Mondays in Epiphanytide the hymns are as follows:

From the Оctave of the Epiphany until the 1st Sunday in Lent - On Mondays:

Mattins: Somno refectis artubus... ... ... 15
Lauds: Splendor Paterne glorie... ... ... 17
Evensong: Immense celi Conditor... ... ... 20

There are in total 21 hymns for this season:  3 different hymns per day, for each day of the week.  Each day's hymns for this period, including texts and audio files, are available at the following links:

• Sunday
• Monday
• Tuesday
• Wednesday
• Thursday
• Friday
• Saturday

The Monday hymn for Mattins during this period is Somno refectis artubus; Hymn melodies prescribes it to be sung to melody #15:

The Liber Hymnarius has a version of this in Latin, sung to melody #15; click the arrow to listen to the mp3:

Somno refectis artubus (saec. VI-VII)
Meter: 8.8.8.8
Melody: d e f g eg f e f

H.IV, p. 190

TPL says this about the hymn:

Attributed to St. Ambrose (340-397). In the current Liturgia Horarum, this hymn is used for the Office of the Readings for Monday of the first and third weeks of the Psalter during Ordinary Time. Likewise it is used in the Roman Breviary for Monday Matins during the same period.

Here are the words in Latin and English; the translation by J. M. Neale (1818-1866):

SOMNO refectis artubus, spreto cubili, surgimus: nobis, Pater, canentibus adesse te deposcimus.	OUR limbs refreshed with slumber now, and sloth cast off, in prayer we bow; and while we sing Thy praises dear, O Father, be Thou present here.
Te lingua primum concinat, te mentis ardor ambiat, ut actuum sequentium tu, Sancte, sis exordium.	To Thee our earliest morning song, to Thee our hearts' full powers belong; and Thou, O Holy One, prevent each following action and intent.
Cedant tenebrae lumini et nox diurno sideri, ut culpa, quam nox intulit, lucis labascat munere.	As shades at morning flee away, and night before the star of day; so each transgression of the night be purged by Thee, celestial Light!
Precamur iidem supplices noxas ut omnes amputes, et ore te canentium lauderis in perpetuum. 1	Cut off, we pray Thee, each offense, and every lust of thought and sense; that by their lips who Thee adore Thou mayest be praised forevermore.
Praesta, Pater piissime, Patrique compar Unice, cum Spiritu Paraclito regnans per omne saeculum. Amen.	Grant this, O Father ever One with Christ, Thy sole-begotten Son, and Holy Ghost, whom all adore, reigning and blest forevermore. Amen.

At Monday Lauds during this period, the prescribed hymn is Splendor paternae gloriae, sung, according to Hymn melodies,  to melody #17:

LLPB  offers this mp3 (in English) of Splen­dor pa­ter­nae glor­i­ae sung to melody #17; they call it "O Splendor of God's Glory Bright."

Here's TPL on this hymn:

Written by St. Ambrose (340-397), this hymn is a companion hymn to his Aeternae rerum Conditor. Splendor paternae gloriae is a beautiful morning hymn asking for help and guidance throughout the day. It is directed to the Trinity, and especially to Christ as the light of the world. The hymn is traditionally sung at Monday Lauds and is used in the Liturgia Horarum at Lauds for Monday of the first and third weeks of the Psalter during Ordinary Time.

Here are the words in Latin and English; the translation is by Poet Laureate Robert Bridges (1844-1930):

SPLENDOR paternae gloriae, de luce lucem proferens, lux lucis et fons luminis, diem dies illuminans.	O splendor of God's glory bright, O Thou that bringest light from light, O Light of Light, light's Living Spring, O Day, all days illumining.
Verusque sol, illabere micans nitore perpeti, iubarque Sancti Spiritus infunde nostris sensibus.	O Thou true Sun, on us Thy glance let fall in royal radiance, the Spirit's sanctifying beam upon our earthly senses stream.
Votis vocemus et Patrem, Patrem perennis gloriae, Patrem potentis gratiae,1 culpam releget lubricam.	The Father too our prayers implore, Father of glory evermore, the Father of all grace and might, to banish sin from our delight:
Informet actus strenuos, dentem retundat invidi, casus secundet asperos, donet gerendi gratiam.2	To guide whate'er we nobly do, with love all envy to subdue, to make ill-fortune turn to fair, and give us grace our wrongs to bear.
Mentem gubernet et regat casto, fideli corpore;3 fides calore ferveat, fraudis venena nesciat.	Our mind be in His keeping placed, our body true to Him and chaste, where only faith her fire shall feed to burn the tares of Satan's seed.
Christusque nobis sit cibus, potusque noster sit fides; laeti bibamus sobriam ebrietatem Spiritus.4	And Christ to us for food shall be, from Him our drink that welleth free, the Spirit's wine, that maketh whole, and mocking not, exalts the soul.
Laetus dies hic transeat; pudor sit ut diluculum, fides velut meridies, crepusculum mens nesciat.	Rejoicing may this day go hence, like virgin dawn our innocence, like fiery noon our faith appear, nor know the gloom of twilight drear.
Aurora cursus provehit: Aurora totus prodeat,5 in Patre totus Filius et totus in Verbo Pater. Amen.	Morn in her rosy car is borne: let Him come forth our Perfect Morn, the Word in God the Father One, the Father perfect in the Son. Amen.

At Monday Vespers, the hymn prescribed by Hymn melodies during this period is Immense caeli conditor, sung to melody #20:

LLPB  offers this mp3 (in English) of Immense caeli conditor sung to this tune; they call it  "O Boundless Wisdom, God Most High."

One really interesting thing about the daily Vespers hymns is that they recapitulate the 7 days of Creation!  For instance,  TPL says this about Immense caeli conditor:

Attributed to Pope St. Gregory the Great (540-604). The theme of this traditional hymn for the second day of the week is fittingly the second day of creation on which the firmament was created (Gen 1, 6-8). The hymn is traditionally sung at Monday Vespers and is used in the Liturgia Horarum at Vespers for Mondays of the first and third weeks of the Psalter during Ordinary Time. Likewise the hymn is also found in the Roman Breviary for Monday Vespers.

Here are the words in Latin and English; the translation is by J. M. Neale (1818-1866):

IMMENSE caeli conditor, qui, mixta ne confunderent, aquae fluenta dividens, caelum dedisti limitem,	O GREAT CREATOR of the sky, Who wouldest not the floods on high with earthly water to confound, but madist the firmament their bound;
Firmans locum caelestibus, simulque terrae rivulis, ut unda flammas temperet, terrae solum ne dissipet:1	The floods above Thou didst ordain; the floods below Thou didst restrain: that moisture might attemper heat, lest the parched earth should ruin meet.
Infunde nunc, piissime, donum perennis gratiae, fraudis novae ne casibus nos error atterat vetus.	Upon our souls, good Lord, bestow Thy gift of grace in endless flow: lest some renewed deceit or wile of former sin should us beguile.
Lucem fides inveniat,2 sic luminis iubar ferat; haec vana cuncta terreat,3 hanc falsa nulla comprimant.	Let faith discover heavinly light; so shall its rays direct us right: and let this faith each error chase, and never give to falsehood place.
Praesta, Pater piissime, Patrique compar Unice, cum Spiritu Paraclito regnans per omne saeculum. Amen.	Grant this, O Father, ever One with Christ, Thy sole-begotten Son, and Holy Ghost, whom all adore, reigning and blest forevermore. Amen.