You can take a break after each section, if you like. A little pop-up will come up asking you if you want to continue to the next block or take a break, after each section.
You can take a break for however long you want in between, you can suspend the exam and walk away if you need to. It's no different from 4 UWorld Qbanks all glued together.
Thanks. Just wanted to make sure as I was considering to do NBME/UWSA back to back over 8 hrs but want to be able to take a break in there along the way 😉