Its a great idea, but i think the concept could work better. For example,would be good to see which users are registered for certain hour or day, because just leaves a message to the user and the admin doesn't know for who that reserve was made.
The Schedule is too simple,should be there more options or to add more specific timing, not only by 15/30/60min periods, coz for example if there is appointments just for 8am-10pm, and 6pm-7pm in a full day, should only appear two options and not all the other hours in such big list to reserve. Also would be nice to be able to select the day of the appointment because the actual calendar it's just to register when was made the user appointment, would be more useful if we could create appointments for certain day and that the calendar would show us the days when that appointments will take place,so that people could select the most appropriate day and register.
But great work and thank you for all your effort.