hey, i'm a d1 at nyu right now. classes start at 8am everyday and generally go until 5pm. some days are busier than others. i have days where i might have a 1 or 2 hour break a couple times between classes. other days, i will have only one break the entire day.
we only started our classes 2 weeks ago, but our main sciences are biochem (called building blocks) and anatomy (called head and neck anatomy, but we cover everything). biochem is about 3-4 lectures a week, and each lecture is usually 2 hours long. anatomy is 2 lectures a week (2 hrs each), and 3 labs a week. then there is general dental simulation I (GDS I) twice a week, where we are in the bench lab for about 3 hours at a time. besides these classes, we have other classes like epidemiology, dentistry as a profession, case presentations, and ethics scattered throughout.
there are a LOT of quizzes, but this only helps students keep up with the material. i'd say we have maybe 6-8 quizzes a week, and exams and practicals every couple of weeks.
as for overlapping classes, i know biochem will end some time in november, but we will also have started cell organelles at some point before then... so that will be 3 big science classes all at once, on top of everything else. i don't think they will overlap for very long, but it does happen. i am not there yet, so this is as much as i can tell u right now. hope it helps!