It is usually necessary to make an appointment(预约) with a doctor, dentist or lawyer. You should call as far in advance as possible. 

A: Would Dr. Block be able to see me at 9:30 tomorrow? 
B: I'm sorry,  she won't have any openings until 11:00, unless there's a cancellation（取消）. 
A: Can she be convenient at 1:00? 
B: Er…..Yes, she's free then. .You can come at that time.
A: Ok, thank you .