I think the 1 hour appointments would be preferred as I think a 30min appointment is more like an hour in length for the escort if you take into account getting ready, showering, dressing and then after booking showering, cleaning up etc.
I have done 30mins bookings when cash was tight just to see my Mistress but the 1 hour booking is the preferred minimum duration. Ideal session is between 2-4 hours, longest session was 9 hours, and that just wizzed by, the longer the better I say.
Service should always be good no matter what duration is booked providing of course the client is being respectful during the appointment.