Ten minutes is not too long to wait.
Real partners can wait ten minutes for a call-back. The requests that can't wait are the ones most worth checking, including the ones that sound like the boss.
The vacation test.
If your bookkeeper took two weeks off tomorrow, what would stop? The answer is the most useful map of your back office you'll draw all year, and it costs nothing.
How do you know?
Every control exists to answer one question. A binder of policies isn't the same as knowing.