I am setting up a booking calendar for students to book time on instruments. I want them to book the instruments for as long as they need them, so let them set the "appointment" length. No staff member needs to be present, so the time booked is only limited to that instrument being available. How do I do this in bookings? They would just need the option to set appointment start and an appointment end times. This does not seem to be currently available. Can this be added or is there another app that allows this?