I have been asked if it was proper to celebrate the feast days of Saints during Lent. The answer is yes. Although Lent is a time of preparation the Easter, the only time during which such celebrations are prohibited is during Holy Week itself. These days focus solely upon the Passion and Death of Our Lord and Savior. This also holds true for the octave of Easter. All of the days from Easter to Low Sunday (Quasimodogeniti) admit no feast whatsoever. For example, if March 25th, the Annunciation, falls during Holy Week (or Easter week) it is always transferred to the first free day after Low Sunday.
This year, St. Matthias Day (February 24) is the Wednesday after Invocabit. At this Mass the Gloria in Excelsis is sung; but the tract replaces the Alleluia Verse. This would be the pattern for any feast celebrated during Lent; but outside of Holy Week.
The historic Gradual is from Psalm 139:17-18 - How precious also are thy thoughts unto me, O God! how great is the sum of them! If I should count them, they are more in number than the sand.
The Tract is from Psalm 21:2-3 - Thou hast given him his heart's desire, and hast not withholden the request of his lips. For Thou hast prevented him with the blessings of goodness: and setest a crown of pure gold on his head.