You have stopped behind a school bus whose red lights are flashing and whose stop arm is extended. When can you pass?

When a school bus has stopped with its red lights flashing and its stop arm extended, you must stop at least 20 feet away no matter which direction you are traveling in. You must remain stopped until the red lights have stopped flashing and the stop arm has been retracted. [Flashing Red Lights, Chapter 4 Sharing the Road, Minnesota Driver's Manual]