Are the rules for fasting and abstinence different during Lent than they are during the rest of the liturgical year?

In their Pastoral Statement on Penance and Abstinence the U.S. bishops state:

10. Beginning with the powerful lesson of Ash Wednesday, Lent has retained its ancient appeal to the penitential spirit of our people. It has also acquired elements of popular piety which we bishops would wish to encourage.

11. Accordingly, while appealing for greater development of the understanding of the Lenten liturgy, as that of Advent, we hope that the observance of Lent as the principal season of penance in the Christian year will be intensified. This is the more desirable because of new insights into the central place in Christian faith of those Easter mysteries for the understanding and enjoyment of which Lent is the ancient penitential preparation.

12. Wherefore, we ask, urgently and prayerfully, that we, as people of God, make of the entire Lenten Season a period of special penitential observance. Following the instructions of the Holy See, we declare that the obligation both to fast and to abstain from meat, an obligation observed under a more strict formality by our fathers in the faith, still binds on Ash Wednesday and Good Friday. No Catholic Christian will lightly excuse himself from so hallowed an obligation on the Wednesday which solemnly opens the Lenten season and on that Friday called "Good" because on that day Christ suffered in the flesh and died for our sins.

13. In keeping with the letter and spirit of Pope Paul's Constitution Poenitemini, we preserved for our dioceses the tradition of abstinence from meat on each of the Fridays of Lent, confident that no Catholic Christian will lightly hold himself excused from this penitential practice.

14. For all other weekdays of Lent, we strongly recommend participation in daily Mass and a self-imposed observance of fasting. In the light of grave human needs which weigh on the Christian conscience in all seasons, we urge, particularly during Lent, generosity to local, national, and world programs of sharing of all things needed to translate our duty to penance into a means of implementing the right of the poor to their part in our abundance. We also recommend spiritual studies, beginning with the Scriptures as well as the traditional Lenten Devotions (sermons, Stations of the Cross, and the rosary), and all the self-denial summed up in the Christian concept of "mortification."

15. Let us witness to our love and imitation of Christ, by special solicitude for the sick, the poor, the underprivileged, the imprisoned, the bedridden, the discouraged, the stranger, the lonely, and persons of other color, nationalities, or backgrounds than our own. A catalogue of not merely suggested but required good works under these headings is provided by Our Blessed Lord Himself in His description of the Last Judgment (Mt 25:34-40). This salutary word of the Lord is necessary for all the year, but should be heeded with double care during Lent.