Schedule unmount of PGP disk

I'd like to schedule for a pgp virtual drive to automatically unmount at a given time each day if it's mounted. Unfortunately I have no idea how to begin. Suggestions? It's okay for the unmount to fail if files in the virtual drive are open or locked but I'd like something in place to automatically unmount it at a given time each day if possible. My motivation is that I've observed that backups of the pgp file fail if the drive is open at the time the backup is run so I'd like to have something in place to close the drive each day before the backup process runs.

Thanks!