Tardy to Study Hall due to Bathroom - 504 Plan

Our 9th grade child just established a 504 Plan for this current high school. He has to use the bathroom more frequently due to medication. He has study hall after lunch. The study hall teacher tells him he cannot use the bathroom during her class, but when he tries to go right before her class she is marking him tardy repeatedly. When I reached out the Vice Principle states he agrees with the study hall teacher and my child needs to go at lunch and hold it before and during her class. I am confused why this is the hill the teacher and the administrator want to die on especially during a non graded period (study hall). Can he be excused from tardies for this period due to either bowels or frequent urination AFTER lunch (not during).