Should we pay nonexempt employees for voluntarily running office errands before work?

Q. Because our office is in a residential area, mail isn’t delivered until the late afternoon. One of our secretaries volunteered to pick up the mail at the post office on her way to work every day. It’s not too far out of the way, but it does change her regular route to work. Are we required to reimburse her for the additional time, as well as mileage?