I am in one now, but I have already finished the MSN portion (my school awards both degrees). It doesn't really save any time. I have a very hard time believing it can be done in 3 years for most people. Mine is 90 credit hours and will take a full 4 years, 9 semesters of full time study 3 of part-time at the very end. I have taken anywhere from 9 to 11 credit hours every semester. Doing it all part-time would easily take 5-6 years.
I am only the 2nd student at my school to go straight through the DNP without NP experience. The program is geared to those in practice, and I am at a significant disadvantage. In fact, I think there is a good chance I will not finish on time b/c I don't have the resources to implement my research project without a job and connections, etc. I think that fact is going to put me behind at least one semester, maybe two, bringing me pretty close to 5 years, 3.5 FT, 1.5 PT. I just don't see how 3 years is possible.
Also, my school is organized in cohorts. Another disadvantage for me is that I entered a cohort that had been together for a year. They all knew each other, and groups for research and projects (which are major, requiring a lot of travel), etc had already formed. It was hard to just jump into established groups. If something comes up and you have to change plans, you won't keep up with your cohort. I think starting and finishing with the same people is invaluable.
I'm an not trying to discourage you, I am a huge supporter of the DNP, obviously. However, I think schools, and the rumor mill, give a lot of people unrealistic expectations. I don't have any regrets, and I wouldn't do anything differently. In your shoes, I think I'd sit down with someone and ask to see the MAT plan, and ask for them to address exactly how a NP candidate with zero practice experience is going to complete their research and capstone project. Just picking a topic without experience is daunting!
I am loving my DNP education. Good luck to you!