I hope this clears some things up.
From the General Instructions on the Liturgy of the Hours.
From the section: Chapter I-IV. Participants in the Liturgy of the Hours under the subheading: Mandate to Celebrate the Liturgy of the Hours
- Hence bishops, priests, and other sacred ministers, who have received from the Church the mandate to celebrate the liturgy of the hours (see no. 17), should recite the full sequence of hours each day, observing as far as possible the true time of day.
They should, first and foremost, attach due importance to those hours that are, so to speak, the two hinges of the liturgy of the hours, that is, morning prayer and evening prayer, which should not be omitted except for a serious reason.
They should faithfully pray the office of readings, which is above all a liturgical celebration of the word of God. In this way they fulfill daily a duty that is peculiarly their own, that is, of receiving the word of God into their lives, so that they may become more perfect as disciples of the Lord and experience more deeply the unfathomable riches of Christ.
In order to sanctify the whole day more completely, they will also treasure the recitation of daytime prayer and night prayer, to round off the whole Opus Dei and to commend themselves to God before retiring.
But this is qualified under this section: Chapter II-V. Daytime Hours
- Vatican Council II decreed that these lesser hours are to be retained in choir.
The liturgical practice of saying these three hours is to be retained, without prejudice to particular law, by those who live the contemplative life. It is recommended also for all, especially those who take part in retreats or pastoral meetings.
- Outside choir, without prejudice to particular law, it is permitted to choose from the three hours the one most appropriate to the time of day, so that the tradition of prayer in the course of the day’s work may be maintained.
So for secular priests they only need to pray one of the Daytime Hours so that makes 5 Hours they should be praying when able.