It depends on your testing center. Some of them have scheduled breaks, usually after each section. Mine did not do this. We were allowed to use the bathroom one at a time when we finished a section. This seemed to work out okay in every section except the math, as most people typically finished early. After I finished the math, I had to use some of my science time to use the bathroom as I finished the math right on time. They give you a ton of time on the science IMO, so it worked out fine. Even with the break, I finished like 20 mins early.