Is my professor allowed to schedule an exam during the semester’s “study period” before finals week?

The whole semester, my course’s syllabus stated that we would have our final exam during finals week. Today, they just made an announcement on Lamaku saying that they has changed the exam date to December 12th. On the academic calendar, it says the last day of instruction is December 11, with December 12 being the study period. Are they allowed to do this?