This is a good question - and here is my answer.
Seriously, I think it would depend on the diocese or religious order that accepts you as a seminarian. Some vocation directors, diocesan bishops, or religious superiors might give a shorter formation time. I remember a seminarian in one diocese with a B.A. in Philosophy who did one year of Pre-Theology instead of two.
The advisor of the Philosophy Department at your college would probably be helpful as well.
Now, before I go any further, I do suggest talking this over with a vocation director of a diocese (or dioceses) or a religious house that you are considering entering formation. There may be some seminarians at your school already that you have class with (i.e. this is common at the University of Dallas - the Pre-Theology seminarians there get the equivalent of a B.A. in Philosophy, and the undergraduate seminarians graduate with a B.A. in Philosophy. ). A vocation director or a religious superior will know much more than a lay person like myself. Also, keep in mind that different dioceses use different seminaries - which could also vary.
Cle_GDP-10: Thanks - and I’m glad you are discerning this vocation.