Part I is not structured in that x amount of time is dedicated for each of the four sections.
Here's a the whole day schedule:
8:30 AM - Reporting/checking in
8:45 AM - Instructions
9 AM - 12:30 PM - Anatomic Sciences and Biochem/Physio
12:30 - 1:30 PM - Lunch/break
1:30 - 5 PM - Micro/Patho and Dental Anatomy
As you can see, you'll have 3.5 hours to finish two sections (200 questions). I'm assuming that you can proceed to the second section once you're finished with first section within the same time block. I'm also assuming that you're able to leave for lunch early if you finished the first two sections before 12:30 PM and leave for good if you finished the last two sections before 5 PM.
I think there will be plenty of time to complete this Part I exam, unlike the DAT where you had to race with the timer in the Reading Comprehension and in the Quantitative Reasoning sections!