I started discerning in one diocese (Los Angeles) and continued discerning in another (Kalamazoo, where my family lives.) This is my experience based on that process:
The formation length of each was the same: four years of philosophy for those without a college degree, or for those with a 4-year degree, 2 years of pre-theology (condensed philosophy without the gen-ed courses.) The philosophy was followed by four years of theological studies, with a year of pastoral assignment between the second and third year, and ordination to the temporary diaconate between the third and fourth theological years. There were usually shorter summer assignments as well between most years.
One graduates with a Masters of Divinity, which in terms of credits is equivalent (or more) to a Doctorate, without the requirement of a doctoral thesis. This is followed by ordination to the priesthood, which is more often than not actually slightly before the end of the last semester.
Based on one’s talents and the needs of the diocese, she may decide to send him for additional studies following your priestly ordination. This may be in whatever the diocese needs you to have you study. You will have to write a doctoral thesis, and defend it, just as he would a secular doctorate. A very common place they would send for this is Rome, but there are others in the US as well. Rome is actually cheaper, minus the transportation costs, which makes it appealing. I don’t know much more than that, because don’t expect any of that to pertain to me.
In my diocese at least, even if you get a “secular” philosophy degree, then decide to pursue seminary formation, we would still be required to take the two years of pre-theology, unless there was a formation program at the school we attended. LA was the same, from what I understood. The reason for this is that the diocese (and the seminaries our diocese uses) require a certain level of spiritual, pastoral, human, and intellectual formation before continuing theology studies. If one attends ‘university’ type school, then only the intellectual formation is developed, which is only one of the “four pillars of formation.”
Our diocese makes use of two seminaries in the US for pre-theology (Detroit and Cleveland), each with a minor seminary (undergrad). Following this, seminarians may continue in the same seminary, go to the other, or be sent to The Pontifical North American College in Rome. We don’t choose, the diocese sends us. LA sent pretty much all of their seminarians to St. John Seminary, but they did not have a minor seminary, and the seminary was in the Archdiocese. Likewise, Detroit sends pretty much all of its seminarians to their own seminary.
There’s my three cents.