Can I take multiple GRE subject tests in the same day? Is it possible for a student to sit for more than one GRE subject test in one sitting? For instance, back in high school, I was able to sit for multiple SAT subject tests in one sitting. I, along with other students, had the option of sitting 1, 2 or 3 tests of our choice. Is there a similar policy for the GRE subject tests?
No, you may only take one test during a single session. Unlike the SAT subject tests, you get three hours to do one test, not the other way around.

Source: I've took a GRE subject test last year.