From the handbook:
We allow students to miss UP TO two hours of rehearsal per week for class/lab conflicts. Conflicting courses must be required for your major and not available at another time. A course conflict form must be completed and the conflict will be double-checked. Band staff may be able to help you switch to a closed section or rearrange your schedule to avoid the conflict. Students with evening classes or labs will be expected to attend rehearsal until 20 minutes before the conflicting class begins, or return within 20 minutes after the class ends. Failure to do so will result in an unexcused absence. If the conflicting class/lab is ever canceled or shortened, you will be expected to attend rehearsal.